Communication system, mobile terminal and access router

ABSTRACT

A new technique is disclosed, by which a mobile terminal after executing handover between subnets can quickly perform packet transmission to outside immediately after the handover. According to this technique, after deciding the execution of handover, MN (mobile terminal)  10  requests an external transmission address (link local address of an access router belonging to a subnet or of a default router after the handover) relating to a subnet connected after the handover at the same time as the transmitting of RtSolPr message to PAR 21  connected before the handover. PAR acquires the external transmission address in response to the request and transmits the external transmission address to MN together with a response by PrRtAdv message to MN. MN sets up the external transmission address as acquired before the handover to the packet to be transmitted after the handover.

TECHNICAL FIELD

The present invention relates to an improvement of technique of fasthandover (Fast Mobile IP; hereinafter referred as “FMIP”) in a mobile IP(Mobile Internet Protocol; hereinafter referred as “MIP”).

BACKGROUND ART

In the past, the technique of FMIP has been known as a technique toprovide effective means for Internet application requiring real time tominimize packet loss, which cannot be prevented by ordinary layer-3handover using MIP technique (e.g. see the Non-Patent Document as givenbelow.) Description will be given below on FMIP by referring FIG. 1,FIG. 41 and FIG. 42.

The radio communication system shown in FIG. 1 includes: IP network(communication network) 15 such as Internet, a plurality of subnets(also called subnetworks) 20 and 30 connected to IP network, a mobileterminal (MN: Mobile Node) 10, which can be connected to one of theplurality of subnets 20 and 30, and CN (Correspondent Node), which iscorrespondent of MN10. In FIG. 1, two subnets 20 and 30 are shown as theplurality of subnets 20 and 30.

The subnet 20 comprises an access router (PAR) 21 for executing therouting to an IP packet (packet data), and a plurality of access points(APs) 22 and 23 for forming inherent radio coverage areas(communicatable areas) 22 and 23. Each of these APs 22 and 23 isconnected to PAR21, and PAR21 is connected to the IP network 15. In FIG.1, two APs 22 and 23 are shown as the plurality of APs 22 and 23. Also,the subnet 30 comprises the same aspect of connection as the subnet 20as described above by an access router (NAR) 31 and a plurality of APs32 and 33.

Here, assumption is made on a case where handover is executed from thesubnet 20 to the subnet 30 when MN10 moves in a radio coverage area 34formed by AP32 via an overlap area 26 from a radio coverage area 25formed by AP23. Hereinafter, the access router, which is present at asuperior position to AP23 and to which MN10 is connected before thehandover, is called PAR (Previous Access Router) 21, and the accessrouter, which is present at a superior position of AP32 and to whichMN10 is connected after the handover, is called NAR (New Access Router)31.

PAR21, i.e. a component element of the subnet 20, and NAR31, i.e. acomponent element of the subnet 30, can communicate with each other viathe IP network 15. That is, the subnet 20 and the subnet 30 areconnected via the IP network 15.

Next, description will be given on operation in FMIP referring toFIG. 1. In FMIP, there are two operation modes, depending on whetherFBAck (Fast Binding Acknowledgement) message is received or not on alink (link before handover), to which MN10 is connected before thehandover. This depends on whether MN10 transmits FBU (Fast BindingUpdate) message or not on a link before the handover. Hereinafter, anoperation mode in case MN10 transmits FBU message on a link before thehandover is called a first operation mode, and an operation mode in caseMN10 does not transmit FBU message on a link before the handover iscalled a second operation mode.

First, description will be given below on the first operation mode, inwhich MN10 transmits FBU message on a link before the handover. FIG. 41is a sequence chart to show general features of the first operation modein FMIP when MN10 transmits FBU message on a link before the handover.

For instance, when MN10 starts to move from an area of PAR21 (radiocoverage area 25 of AP23) to an area of NAR31 (radio coverage area 34 ofAP32), the movement is detected by a layer 2, and the handover in thelayer 3 as starting point is initiated. This initiation of the handoveris determined through comparison of the intensity of the receivedelectric field from AP23 with that of the electric field from AP32 inthe overlap area 26.

When information including AP-ID (identification information of each AP)of AP32, which is the destination of movement, is notified from thelayer 2, MN10 transmits an RtSolPr (Router Solicitation for Proxy)message including AP-ID of AP32 to PAR21 currently connected (StepS801). Upon receipt of the RtSolPr message, PAR21 retrieves an accessrouter existing in the neighborhood according to AP-ID of AP32 asnotified from MN10 and acquires the information of NAR31, or it acquiresthe information of NAR31 from the information already retrieved(information retained by PAR21).

Then, PAR21 transmits a PrRtAdv (Proxy Router Advertisement) messageincluding the information of NAR31 (e.g. link layer address of NAR31, ornetwork prefix of the subnet 30, to which NAR31 belongs) to MN10 as aresponse to the RtSolPr message (Step S803).

Upon receipt of this PrRtAdv message, MN10 generates NCoA (New Care-ofAddress), which is an address adaptable at the subnet 30 by using thenetwork prefix of the subnet 30 included in the PrRtAdv message and thelink layer address of MN10 itself, and FBU message including NCoA istransmitted to PAR21 (Step S805).

Upon receipt of the FBU message, PAR21 transmits an HI (HandoverInitiate) message including NCoA to NAR31 in order to confirm whetherthe NCoA generated at MN10 is an address usable at the subnet 30 or not(Step S807). When the HI message is received, NAR31 verifies whether theNCoA included in the HI message is effective or not. In case NCoA iseffective, HAck (Handover Acknowledge) message to specify the statusshowing the result is transmitted to PAR21 (Step S809). When the HAckmessage is received, PAR21 transmits FBAck message to notify the resultto MN10 and NAR31 (Steps S811 and S813). Then, the packet sent to MN10is forwarded to NAR31 (Step S815). When the packet to MN10 has beenforwarded from PAR21, NAR31 performs buffering of the packet.

Then, MN10 initiates actual moving to the subnet 30 and executes thehandover from AP23 to AP32, for instance (Step S817). Immediately afterconnection switchover to NAR31, an FNA (Fast Neighbor Advertisement)message to request the notification of connection to NAR31 and thetransmission of the packet processed by buffering is transmitted toNAR31 (Step S819). Upon receipt of FNA message, NAR31 transmits thepacket processed by buffering to MN10 (Step S821).

Next, description will be given on the second operation mode, in whichMN10 does not transmit the FBU message on a link before the handover andtransmits FNA (message including FBU) on a link after the handover. FIG.42 is a sequence chart to show general features of the second operationmode in FMIP when MN10 in the conventional technique transmits FNA [FBU]message on a link after the handover in the conventional technique(prior art).

Similarly to the first operation mode shown in FIG. 41, MN10 transmitsRtSolPr message (Step S901) and receives PrRtAdv message (Step S903).Then, without transmitting the FBU message in the first operation modeshown in FIG. 41 (Step S805 in FIG. 41), actual moving to the subnet 30is initiated. For instance, L2 handover is executed from AP23 to AP32(Step S905).

Then, immediately after the connection switchover to NAR31, MN10transmits the FNA message including FBU message in it (this message isdescribed as FNA [FBU]) to NAR31 (Step S907). NAR31 verifies theeffectiveness of NCoA included in the FNA message (Step S909). In caseNCoA is effective, the FBU message is transmitted to PAR21 (Step S911).In case NCoA is not effective, NAAck (Neighbor AdvertisementAcknowledgement) message to notify that NCoA cannot be used is sent toMN10.

As a response to this FBU message, PAR21 transmits FBAck message toNAR31 (Step S913) and forwards the packet addressed to MN10 to NAR31(Step S915). NAR31 receives FBAck message from PAR21 and forwards thepacket addressed to MN10 as received from PAR21 to MN10 (Step S917).

In the Non-Patent Document 1 as given below, it is suggested that IPv6address of NAR31 is set as the destination address of the FNA messagewhen the FNA message is sent to NAR31. In view of the fact that thesetting of NCoA is given as the address of transmission source of theFNA message, there is no disclosure on the procedure, by which it can beestimated that IPv6 address of NAR31 is a global IP address (there is nodisclosure on the procedure, by which NAR31 acquires global IPv6address) or it is a multi-cast address in the subnet 30.

[Non-Patent Document 1] Rajeev Koodli; “Fast Handovers for Mobile IPv6”,draft-ietf-mobileip-fast-mipv6-08, October 2003.

[Non-Patent Document 2] T. Narten, E. Nordmark and W. Simpson: “NeighborDiscovery for IP Version 6 (IPv6)”, RFC2461, December 1998.

However, according to the technique disclosed in the Non-Patent Document1, MN10 can quickly receive the packet immediately after the handover byperforming the acquisition and the registration (Binding Update) of NCoAbefore or immediately after the handover, while due consideration is notgiven to the quick transmission of the packet by MN10 after thehandover.

FIG. 43 shows a routing table to explain a first example of the problemin the conventional FMIP technique. To transmit the packet to outsidefrom inside of the subnets 20 and 30, MN10 refers to the routing table.FIG. 43 shows the routing table before MN10 carried out the handover.When the packet is transmitted to outside (e.g. CN40) under thecondition that MN10 before the handover is connected with the subnet 30,the entry relating to a default router (a router set in such manner thatthe packet can be sent to outside from within the subnet 20) is hit fromthe transmission destination of the packet, and then, the entry wherethe link local address of PAR21 specified to the gateway of the entry isset to the destination is hit. As a result, MAC address of PAR21specified to the gateway of the entry is set as the destination addressof Ethernet (registered trademark) of the packet. FIG. 43 shows therouting table where the default router of the subnet 20 is the same asPAR21.

On the other hand, in order that MN10 transmits the packet from withinthe subnet 30 after the handover, the link local address of NAR31 or thelink local address of the default router 37 of the subnet 30 must be setup as a default router in the routing table of MN10. However, despite ofthe fact that MN10 can acquire new CoA (NCoA) by FMIP before thehandover, the default router in the subnet 20 before the handover isstill set up as the default router of MN10 after the handover in therouting table. In this respect, the packet to be sent to outside fromthe subnet 30 is abandoned without being sent from the subnet 30. Evenwhen MN10 attempts to update the routing table immediately after thehandover, it is not possible to update the routing table because NAR31of the subnet 30, which is a new destination of connection or the linklocal address of the default router 37 is not known.

On the other hand, in the Non-Patent Document 2 as given above, it isdisclosed that MN10 can acquire the external transmission address asdescribed in the RA message (the link local address of NAR31 as givenabove or the link local address of the default router 37 of the subnet30) by receiving an RA (Router Advertisement) message from NAR31 or thedefault router 37. Also, in the RA message, information to identify thedefault router 37 is also described. However, the RA message is themessage to be sent out periodically from each router, and it issubstantially difficult that MN10 transmits the packet to outside (e.g.CN40) until MN10 passively receives RA message and acquires the externaltransmission address. Similarly, besides the external transmissionaddress as given above, there is no procedure to acquire the informationincluded in the RA message, which can be received at the subnet 30except that the RA message is passively received while being in standbyafter the handover.

In case MN10 may have the global IPv6 address of NAR31 of the subnet 30before the handover, the packet transmitted from MN10 immediately afterthe handover can reach CN40 if encapsulation of the packet as shown inFIG. 44 is carried out by MN10. However, various prescriptions must benewly set up such as conversion of header at NAR31 or de-encapsulationof the packet at PAR21, and this requires modification of the totalcommunication system, and it is not a very realistic solution.

In FMIP, it is possible to acquire network prefix of the subnet 30 andthe link layer address of NAR31, and it is possible to estimate the linklocal address of NAR31 from such types of information. However, evenwhen the link local address of NAR31 can be estimated, it is necessaryto confirm whether it is used (or it is correct) or not, and this meansthat time is required for confirmation. Also, it is possible to estimatethe link local address of NAR31 but it is entirely impossible toestimate the link local address of the default router 37 existing in thesubnet 30.

DISCLOSURE OF THE INVENTION

To solve the above problems, it is an object of the present invention toprovide a communication system, a mobile terminal, and an access router,in which the mobile terminal carrying out the handover between subnetscan quickly execute packet transmission to outside immediately after thehandover.

To attain the above object, the present invention provides acommunication system, which comprises a first access router belonging toa first subnet and a second access router belonging to a second subnet,said first access router and said second access router being connectedvia IP network, and a mobile terminal is connected to said first subnetand said second subnet via radio communication, wherein:

the mobile terminal connected to said first subnet requests a link localaddress of said second access router in said second subnet to said firstaccess router under the condition being connected to said first subnetafter deciding that handover to said second subnet is to be executed,and said first access router provides said link local address of saidsecond access router to said mobile terminal.

With the arrangement as described above, the mobile terminal can acquirein advance a link local address of an access router of a subnet athandover destination before executing the handover.

Also, to attain the above object, the present invention provides thecommunication system as described above, which comprises a first accessrouter belonging to a first subnet and a second access router belongingto a second subnet, said first access router and said second accessrouter being connected via IP network, and a mobile terminal isconnected to said first subnet and said second subnet via radiocommunication, wherein:

the mobile terminal connected to said first subnet requests a link localaddress of a default router in said second subnet to said first accessrouter under the condition being connected to said first subnet afterdeciding that handover is to be executed to said second subnet, and saidfirst access router provides said link local address of said defaultrouter to said mobile terminal.

With the arrangement as described above, the mobile terminal can acquirein advance a link local address of a default router of a subnet athandover destination before executing the handover.

Further, the present invention provides the communication system withthe arrangement as described above, wherein said first access routerprovides information included in an RA message sent within said secondsubnet by said second access router together with said link localaddress of said second access router to said mobile terminal.

With the arrangement as described above, the mobile terminal can acquirein advance information included in an RA message of an access router ofa subnet at handover destination before executing the handover.

Also, the present invention provides the communication system asdescribed above, wherein said first access router provides informationincluded in an RA message sent within said second subnet by said defaultrouter together with said link local address of said default router tosaid mobile terminal.

With the arrangement as described above, the mobile terminal can acquirein advance information included in an RA message of a default router ofa subnet at handover destination before executing the handover.

Further, the present invention provides the communication system asdescribed above, wherein said mobile terminal refers to said link localaddress when packet transmission is performed to outside of said secondsubnet after handover is executed from said first subnet to said secondsubnet.

With the arrangement as described above, the mobile terminal afterexecuting the handover between subnets by using the link local addressas acquired can quickly perform packet transmission to outside after thehandover.

Also, the present invention provides the communication system asdescribed above, wherein said mobile terminal requests said link localaddress to said first access router when transmitting a message P torequest information relating to said second access router.

With the arrangement as described above, the mobile terminal can requesta link local address when transmitting a message P to an access routerof a subnet connected before the handover.

Further, the present invention provides the communication system asdescribed above, wherein said mobile terminal is arranged to addinformation to instruct a request of said link local address in saidmessage P, said first access router acquires said link local addressrelating to a subnet specified by information in said message P andtransmits a message Q including said link local address to said mobileterminal by incorporating said link local address in the message Q,which is a response message of said message P.

With the arrangement as described above, the mobile terminal cantransmit the message P including a request of the link local address toan access router of a subnet connected before the handover and canacquire the link local address relating to the subnet after the handoverby receiving the message Q including the link local address from theaccess router of the subnet connected before the handover.

Also, the present invention provides the communication system asdescribed above, wherein said mobile terminal is arranged to transmitinformation to request said link local address different from saidmessage P to said first access router, said first access router isarranged to acquire said link local address relating to a subnetspecified by at least one of information to request said link localaddress and information in said message P received from said mobileterminal and transmits a notifying message including said link localaddress to said mobile terminal by incorporating said link local addressin a notifying message different form the message Q, which is a responsemessage of said message P.

With the arrangement as described above, the mobile terminal can acquirethe link local address relating to the subnet at handover destination bytransmitting information to request the link local address differentfrom the message P to the access router of the subnet connected beforethe handover and by receiving the information including the link localaddress different from the message Q.

Further, the present invention provides the communication system asdescribed above, wherein said mobile terminal is arranged to addinformation to instruct a request of said link local address in saidmessage P, and said first access router acquires said link local addressrelating to a subnet specified by at least one of information to requestsaid link local address and information in said message P received fromsaid mobile terminal and transmits a notifying message including saidlink local address to said mobile terminal by incorporating said linklocal address in a notifying message different from a message Q, whichis a response message of said message P.

With the arrangement as described above, the mobile terminal can acquirethe link local address relating to the subnet after the handover bytransmitting the message P including a request of the link local addressto the access router of the subnet connected before the handover and byreceiving information including the link local address different fromthe message Q from the access router of the subnet connected before thehandover.

Also, the present invention provides the communication system asdescribed above, wherein said mobile terminal is arranged to transmitinformation to request said link local address different from saidmessage P to said first access router, and said first access routeracquires said link local address relating to a subnet specified byinformation in said message P and transmits said message Q includingsaid link local address to said mobile terminal by incorporating saidlink local address in the message Q, which is a response message of saidmessage P.

With the arrangement as described above, the mobile terminal can acquirethe link local address relating to the subnet after the handover bytransmitting information to request a link local address different fromthe message P to an access router of a subnet connected before thehandover and by receiving a message Q including the link local addressfrom the access router of the subnet connected before the handover.

Further, the present invention provides the communication system asdescribed above, wherein said first access router acquires said linklocal address relating to a subnet specified by information in saidmessage when a message P to request information relating to said secondaccess router is received from said mobile terminal and transmits saidmessage Q including said link local address to said mobile terminal byincorporating said link local address in the message Q, which is aresponse message of said message P.

With the arrangement as described above, the mobile terminal can acquirethe link local address of the subnet after the handover by transmittingthe message P to the access router of the subnet connected before thehandover and by receiving the message Q including the link local addressfrom the access router of the subnet connected before the handover.

Also, the present invention provides the communication system asdescribed above, wherein said first access router acquires said linklocal address relating to a subnet specified by information in saidmessage P when said message P is received from said mobile terminal,acquires said link local address and transmits a notifying messageincluding said link local address to said mobile terminal byincorporating said link local address in a notifying message differentfrom a message Q, which is a response message of said message P.

With the arrangement as described above, the mobile terminal can acquirethe link local address relating to the subnet after the handover bytransmitting the message P to the access router of the subnet connectedbefore the handover and by receiving information including the linklocal address different from the message Q from the access router of thesubnet connected before the handover.

Further, the present invention provides the communication system asdescribed above, wherein said mobile terminal is arranged to requestsaid link local address to said first access router when transmitting amessage R to request to forward a packet addressed to said mobileterminal to said second access router.

With the arrangement as described above, the mobile terminal can requestthe link local address when transmitting the message R to the accessrouter of the subnet connected before the handover.

Also, the present invention provides the communication system asdescribed above, wherein said mobile terminal is arranged to addinformation to request said link local address in said message R, saidfirst access router acquires said link local address relating to asubnet specified by at least one of information in said message R, themessage P to request information relating to said second access router,and information in said message P received from said mobile terminalalready before the receiving of said message R and transmits saidmessage S including said link local address to said mobile terminal byincorporating said link local address in a message S, which is aresponse message of said message R.

With the arrangement as described above, the mobile terminal can acquirethe link local address relating to the subnet after the handover bytransmitting the message R including the request of the link localaddress to the access router of the subnet connected before the handoverand by receiving the message S including the link local address from theaccess router of the subnet connected before the handover.

Further, the present invention provides the communication system asdescribed above, wherein said mobile terminal is arranged to transmitinformation to request said link local address different from saidmessage R to said first access router, said first access router acquiressaid link local address relating to a subnet specified by at least oneof information to request said link local address, information in saidmessage R received from said mobile terminal, a message P to requestinformation relating to said second access router, and information insaid message P received from said mobile terminal already before thereceiving of said message R, and transmits a notifying message includingsaid link local address to said mobile terminal by incorporating saidlink local address in a notifying message different from the message S,which is a response message of said message R.

With the arrangement as described above, the mobile terminal can acquirethe link local address relating to the subnet after the handover bytransmitting information to request a link local address different fromthe message R to the access router of the subnet connected before thehandover and by receiving information including the link local addressdifferent from the message S from the access router of the subnetconnected before the handover.

Also, the present invention provides the communication system asdescribed above, wherein said mobile terminal is arranged to addinformation to request said link local address in said message R, andsaid first access router acquires said link local address relating to asubnet specified by at least one of information to request said linklocal address, information in said message R received from said mobileterminal, a message P to request information relating to said secondaccess router, and information in said message P received from saidmobile terminal already before the receiving of said message R, andtransmits a notifying message including said link local address to saidmobile terminal by incorporating said link local address in a notifyingmessage different from the message S, which is a response message ofsaid message R.

With the arrangement as described above, the mobile terminal can acquirethe link local address of the subnet after the handover by transmittingthe message R including a request of the link local address to theaccess router of the subnet connected before the handover and byreceiving information including the link local address different fromthe message S from the access router of the subnet connected before thehandover.

Further, the present invention provides the communication system asdescribed above, wherein said mobile terminal is arranged to transmitinformation to request said link local address different from saidmessage to said first access router, and said first access routeracquires said link local address relating to a subnet specified by atleast one of information in said message R, information of the message Pto request information relating to said second access router, andinformation in said message P received from said mobile terminal alreadybefore the receiving of said message R, and transmits said message Sincluding said link local address to said mobile terminal byincorporating said link local address in the message S, which is aresponse message of said message R.

With the arrangement as described above, the mobile terminal can acquirethe link local address relating to the subnet after the handover bytransmitting information to request a link local address different fromthe message R to the access router of the subnet connected before thehandover and by receiving the message S including the link local addressfrom the access router of the subnet connected before the handover.

Also, the present invention provides the communication system asdescribed above, wherein said first access router acquires, when saidmessage R is received from said mobile terminal, said link local addressrelating to a subnet specified by at least one of information in saidmessage R, a message P to request information relating to said secondaccess router, and information in said message P received from saidmobile terminal already before the receiving of said message R, andtransmits said message S including said link local address to saidmobile terminal by incorporating said link local address in a message S,which is a response message of said message R.

With the arrangement as described above, the mobile terminal can acquirethe link local address relating to the subnet after the handover bytransmitting the message R to the access router of the subnet connectedbefore the handover and by receiving the message S including the linklocal address from the access router of the subnet connected before thehandover.

Further, the present invention provides the communication system asdescribed above, wherein said first access router acquires, when saidmessage R is received from said mobile terminal, said link local addressrelating to a subnet specified by at least one of information in saidmessage R, information in the message P to request information relatingto said second access router, and information in said message P receivedfrom said mobile terminal already before the receiving of said messageR, and transmits a notifying message including said link local addressto said mobile terminal by incorporating said link local address to anotifying message different from a message S, which is a responsemessage of said message R.

With the arrangement as described above, the mobile terminal can acquirethe link local address relating to the subnet after the handover bytransmitting the message R to the access router of the subnet connectedbefore the handover and by receiving information including the linklocal address different from the message S from the access router of thesubnet connected before the handover.

Also, the present invention provides the communication system asdescribed above, wherein said first access router is arranged to requestsaid link local address to said second access router when transmitting amessage T to request the initiation of processing of the handoverrelating to said mobile terminal.

With the arrangement as described above, the mobile terminal can requestthe link local address when transmitting the message T to the accessrouter of the subnet after the handover by the access router connectedbefore the handover.

Further, the present invention provides the communication system asdescribed above, wherein said first access router is arranged to addinformation to request said link local address in said message T, andsaid second access router acquires said link local address relating tosaid second subnet, to which said second access router belongs, andtransmits said message U including said link local address to said firstaccess router by incorporating said link local message in the message U,which is a response message of said message T.

With the arrangement as described above, the access router connectedbefore the handover by the mobile terminal can acquire the link localaddress relating to the subnet after the handover by transmitting themessage T including the link local address to the access router of thesubnet connected after the handover and by receiving the message Uincluding the link local address from the access router of the subnetconnected after the handover by the mobile terminal.

Also, the present invention provides the communication system asdescribed above, wherein said first access router is arranged totransmit information to request said link local address different fromsaid message T to said second access router, said second access routeracquires said link local address relating to said second subnet, towhich said second access route belongs, and transmits a notifyingmessage including said link local address to said first access router byincorporating said link local address in a notifying message differentfrom a message U, which is a response message of said message T.

With the arrangement as described above, the access router connectedbefore the handover by the mobile terminal can acquire the link localaddress relating to the subnet after the handover by transmittinginformation to request the link local address different from the messageT to the access router of the subnet connected after the handover bymobile terminal and by receiving information including a link localaddress different from the message U from the access router of thesubnet connected after the handover by the mobile terminal.

Further, the present invention provides the communication system asdescribed above, wherein said first access router is arranged to addinformation to request said link local address in said message T, andsaid second access router acquires said link local address relating tosaid second subnet, to which said second access router belongs, andtransmits a notifying message including said link local address to saidfirst access router by incorporating said link local address in anotifying message different from the message U, which is a responsemessage of said message T.

With the arrangement as described above, the access router connectedbefore the handover by the mobile terminal can acquire the link localaddress relating to the subnet after the handover by transmitting themessage T including a request of the link local address to the accessrouter of the subnet connected after the handover by the mobile terminaland by receiving information including the link local address differentfrom the message U from the access router of the subnet connected afterthe handover by the mobile terminal.

Also, the present invention provides the communication system asdescribed above, wherein said first access router is arranged totransmit information to request said link local address different fromsaid message T to said second access router, and said second accessrouter acquires said link local address relating to said second subnet,to which said second access router belongs, and transmits said message Uincluding said link local address to said first access router byincorporating said link local address in the message U, which is aresponse message of said message T.

With the arrangement as described above, the access router connectedbefore the handover by the mobile terminal can acquire the link localaddress relating to the subnet after the handover by transmittinginformation to request a link local address different from the message Tto the access router of the subnet connected after the handover by themobile terminal and by receiving the message U including the link localaddress from the access router of the subnet connected after thehandover by the mobile terminal.

Further, the present invention provides the communication system asdescribed above, wherein said second access router acquires, when saidmessage T is received from said first access router, said link localaddress relating to said second subnet, to which said second accessrouter belongs, and transmits said message including said link localaddress to said first access router by incorporating said link localaddress to the message U, which is a response message of said message T.

With the arrangement as described above, the access router connectedbefore the handover by the mobile terminal can acquire the link localaddress relating to the subnet after the handover by transmitting themessage T to the access router of the subnet connected after thehandover by the mobile terminal and by receiving the message U includingthe link local address from the access router of the subnet connectedafter the handover by the mobile terminal.

Also, the present invention provides the communication system asdescribed above, wherein said second access router acquires, when saidmessage T is received from said first access router, said link localaddress relating to said second subnet, to which said second accessrouter belongs, and transmits said message including said link localaddress to said first access router by incorporating said link localaddress to the message U, which is a response message of said message T.

With the arrangement as described above, the access router connectedbefore the handover by the mobile terminal can acquire the link localaddress relating to the subnet after the handover by transmitting themessage T to the access router of the subnet connected after thehandover by the mobile terminal and by receiving information includingthe link local address different from the message U from the accessrouter of the subnet connected after the handover.

Further, the present invention provides the communication system asdescribed above, wherein a first access router belonging to a firstsubnet and a second access router belonging to a second subnet, saidfirst access router and said second access router being connected via IPnetwork, and a mobile terminal is connected to said first subnet andsaid second subnet via radio communication, wherein:

under the condition that said mobile terminal is connected to said firstsubnet, said first access router transmits a message W to instruct theexecution of handover to said second subnet including said link localaddress of said second access router to said mobile terminal.

With the arrangement as described above, the mobile terminal can acquirein advance the link local address of the access router of the subnet athandover destination.

Also, the present invention provides the communication system asdescribed above, wherein a first access router belonging to a firstsubnet and a second access router belonging to a second subnet, saidfirst access router and said second access router being connected via IPnetwork, and a mobile terminal is connected to said first subnet andsaid second subnet via radio communication, wherein:

under the condition that said mobile terminal is connected to said firstsubnet, said first access router transmits a message W including saidlink local address of a default router in said second subnet andinstructing the execution of handover to said second subnet.

With the arrangement as described above, the mobile terminal can acquirein advance the link local address of a default router of the subnet athandover destination before executing the handover.

Further, the present invention provides the communication system asdescribed above, wherein said first access router is arranged to provideinformation included in an RA message sent in said second subnet by saidsecond access router together with said link local address of saidsecond access router to said mobile terminal.

With the arrangement as described above, the mobile terminal can acquirein advance information included in an RA message of the access router ofthe subnet at handover destination before executing the handover.

Also, the present invention provides the communication system asdescribed above, wherein said first access router is arranged to provideinformation included in an RA message sent in said second subnet by saiddefault router together with said link local address of said defaultrouter to said mobile terminal.

With the arrangement as described above, the mobile terminal can acquirein advance information included in an RA message of a default router ofthe subnet at handover destination before executing the handover.

Further, the present invention provides the communication system asdescribed above, wherein said mobile terminal is arranged to refer tosaid link local address when transmitting a packet to outside of saidsecond subnet after executing the handover from said first subnet tosaid second subnet.

With the arrangement as described above, the mobile terminal can acquirein advance information included in an RA message of a default router ofthe subnet at handover destination before executing the handover.

Also, according to the present invention, a mobile terminal and anaccess router included in the communication system as described abovecan be provided.

As the message P as described above, an RtSolPr message to notifyidentification information (AP-ID) of access point at handoverdestination of a mobile terminal (MN) may be used to request information(AR-INFO) relating to an access router (NAR) of the subnet connected bythe mobile terminal (MN) before the handover in FMIP, for instance.

Further, as the message Q as described above, a PrRtAdv message may beused, which is to notify information relating to NAR by PAR to MN inFMIP.

Also, as the message R as described above, an FBU message may be used,which is to notify NCoA generated by MN for the purpose of requestingthe initiation of packet forwarding by MN to NAR in FMIP, for instance.

Also, as the message S as described above, an FBAck message may be used,which is to notify the result of verification of NCoA received from NARto MN by PAR in FMIP, for instance.

Further, as the message T as described above, an HI message may be used,which is to confirm the effectiveness of NCoA notified from MN to NAR byPAR in FMIP, for instance.

Further, as the message U as described above, an HAck message may beused, which is to notify the result of verification of the effectivenessof NCoA of MN notified from PAR to PAR in FMIP, for instance.

Also, as the message W as described above, an unsolicited PrRtAdvmessage to instruct the execution of the handover to the specific subnetmay be used, which includes information relating to the specific subnetby PAR to MN in FMIP, for instance.

The communication system, the mobile terminal, and the access router ofthe present invention have the arrangement as described above, and sucheffects can be provided that the mobile terminal executing the handoverbetween subnets can quickly transmit packet to outside immediately afterthe handover

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematical drawing to show an arrangement of a radiocommunication system commonly used in the present invention and in theconventional technique (prior art);

FIG. 2 is a sequence chart showing principal processing common to afirst embodiment to a fourth embodiment of the present invention;

FIG. 3 is a block diagram to show an example of arrangement of PAR inthe first embodiment of the present invention;

FIG. 4A represents diagrams showing information to request externaltransmission address from MN to be processed in PAR as shown in FIG. 3;

FIG. 4B is a diagram to show an example of data arrangement ofinformation to notify the external transmission address transmitted toMN and processed in PAR shown in FIG. 3;

FIG. 5 is a block diagram to show an example of arrangement of PAR inthe second embodiment of the invention;

FIG. 6A represents diagrams to show information to request the externaltransmission address from MN to be processed in PAR shown in FIG. 5;

FIG. 6B represents diagrams to show an example of data arrangement ofinformation to notify the external transmission address transmitted toMN and processed in PAR shown in FIG. 5;

FIG. 7 is a block diagram to show an example of arrangement of PAR in athird embodiment of the present invention;

FIG. 8A represents diagrams to show information to request the externaltransmission address from MN as to be processed in PAR shown in FIG. 7;

FIG. 8B represents a diagram to show an example of data arrangement ofinformation to notify the external transmission address transmitted toMN and processed in PAR shown in FIG. 7;

FIG. 9 is a block diagram to show an example of arrangement of PAR in afourth embodiment of the present invention;

FIG. 10A represents diagrams to show information to request the externaltransmission address from MN to be processed in PAR shown in FIG. 9;

FIG. 10B represents diagrams to show an example of data arrangement ofinformation to notify the external transmission address transmitted toMN and processed in PAR shown in FIG. 9;

FIG. 11 is a block diagram to show an example of arrangement of MN inthe fourth embodiment of the present invention;

FIG. 12 is a sequence chart to show principal processing common to fifthto eighth embodiments of the present invention;

FIG. 13 is a block diagram to show an example of arrangement of PAR inthe fifth embodiment of the present invention;

FIG. 14A represents diagrams to show information to request the externaltransmission address from MN to be processed in PAR shown in FIG. 13;

FIG. 14B represents a diagram to show an example of data arrangement ofinformation to notify the external transmission address transmitted toMN and processed in PAR shown in FIG. 13;

FIG. 15 is a block diagram to show an example of arrangement of PAR in asixth embodiment of the present invention;

FIG. 16A represents diagrams to show information to request the externaltransmission address from MN to be processed in PAR shown in FIG. 15;

FIG. 16B represents diagrams to show an example of data arrangement ofinformation to notify the external transmission address transmitted toMN and processed in PAR shown in FIG. 15;

FIG. 17 is a block diagram to show an example of arrangement of PAR in aseventh embodiment of the present invention;

FIG. 18A represents diagrams to show information to request the externaltransmission address from MN as to be processed in PAR shown in FIG. 17;

FIG. 18B is a diagram to show an example of data arrangement ofinformation to notify the external transmission address transmitted toMN and processed in PAR shown in FIG. 17;

FIG. 19 is a block diagram to show an example of arrangement of PAR inan eighth embodiment of the present invention;

FIG. 20A represents diagrams to show request information of the externaltransmission address from MN as to be processed in PAR shown in FIG. 19;

FIG. 20B represents diagrams to show an example of data arrangement of anotifying information of the external transmission address to betransmitted to MN and processed in PAR shown in FIG. 19;

FIG. 21 is a sequence chart to show principal processing common to ninthto twelfth embodiments of the present invention;

FIG. 22 is a block diagram to show an example of arrangement of PAR inthe ninth embodiment of the present invention;

FIG. 23 is a block diagram to show an example of arrangement of NAR inthe ninth embodiment of the present invention;

FIG. 24A represents diagrams to show request information of the externaltransmission address to be given and taken between PAR shown in FIG. 22and NAR shown in FIG. 23;

FIG. 24B is a diagram to show an example of data arrangement of anotifying information of the external transmission address to be givenand taken between PAR shown in FIG. 22 and NAR shown in FIG. 23;

FIG. 25 is a block diagram to show an example of arrangement of PAR in atenth embodiment of the present invention;

FIG. 26 is a block diagram to show an example of arrangement of NAR inthe tenth embodiment of the present invention;

FIG. 27A represents diagrams to show request information of the externaltransmission address to be given and taken between PAR shown in FIG. 25and NAR shown in FIG. 26;

FIG. 27B represents diagrams to show an example of data arrangement of anotifying information of the external transmission address to be givenand taken between PAR shown in FIG. 25 and NAR shown in FIG. 26;

FIG. 28 is a block diagram to show an example of arrangement of PAR inan eleventh embodiment of the present invention;

FIG. 29 is a block diagram to show an example of arrangement of NAR inthe eleventh embodiment of the present invention;

FIG. 30A represents diagrams to show request information of the externaltransmission address to be given and taken between PAR shown in FIG. 28and NAR shown in FIG. 29;

FIG. 30B is a diagram to show an example of data arrangement of anotifying information of the external transmission address to be givenand taken between PAR shown in FIG. 28 and NAR shown in FIG. 29;

FIG. 31 is a block diagram to show an arrangement of PAR in a twelfthembodiment of the present invention;

FIG. 32 is a block diagram to show an example of arrangement of NAR inthe twelfth embodiment of the present invention;

FIG. 33A represents diagrams to show request information of the externaltransmission address to be given and taken between PAR shown in FIG. 31and NAR shown in FIG. 32;

FIG. 33B represents diagrams to show an example of data arrangement of anotifying information of the external transmission address to be givenand taken between PAR shown in FIG. 31 and NAR shown in FIG. 32;

FIG. 34 is a sequence chart to show principal processing common tothirteenth and fourteenth embodiments of the present invention;

FIG. 35 is a block diagram to show an example of arrangement of NAR inthe thirteenth embodiment of the present invention;

FIG. 36A represents diagrams to show request information of the externaltransmission address from MN to be processed in NAR shown in FIG. 35;

FIG. 36B represents a diagram to show an example of data arrangement ofa notifying information of the external transmission address to betransmitted to MN and processed in NAR shown in FIG. 35;

FIG. 37 is a block diagram to show an example of arrangement of NAR inthe fourteenth embodiment of the present invention;

FIG. 38A represents diagrams to show request information of the externaltransmission address from MN to be processed in NAR shown in FIG. 37;

FIG. 38B is a diagram to indicate an example of data arrangement of anotifying information of the external transmission address to betransmitted to MN and processed in NAR shown in FIG. 37;

FIG. 39 is a block diagram to show an example of arrangement of MN inthe fourteenth embodiment of the present invention;

FIG. 40 is a sequence chart to show principal processing in a fifteenthembodiment of the present invention;

FIG. 41 is a sequence chart to show general features of a firstoperation mode in FMIP in case MN10 in the conventional techniquetransmits an FBU message by a link before the handover;

FIG. 42 is a sequence chart to show general features of a secondoperation mode in FMIP in case MN10 in the conventional technique (priorart) transmits an FNA [FBU] message in a link after the handover;

FIG. 43 is a table to explain a first example of the problems inconventional FMIP technique; and

FIG. 44 represents diagrams to explain a second example of the problemin the conventional FMIP technique.

BEST MODE FOR CARRYING OUT THE INVENTION

Description will be given below on the first to the fifteenthembodiments of the present invention referring to the drawings. Thearrangement of a radio communication system as shown in FIG. 1 used inthe explanation of the prior art is also referred in the explanation inthe first to the fifteenth embodiments of the present invention.Specifically, assumption is made on a case where the handover from asubnet 20 to a subnet 30 is carried out when MN10, in communication withCN40, moves from a radio coverage area 25 formed by AP23 to a radiocoverage area 34 by AP32 via an overlap area 26.

In the first to the twelfth embodiments as given below, description willbe given on a procedure, by which MN10 acquires an external transmissionaddress (a link local address of NAR31 or a link local address of adefault router 37 belonging to the subnet 30) relating to the subnet 30connected after the handover on a link of the subnet 20 connected beforethe handover. In the thirteenth to the fifteenth embodiments as givenbelow, description will be given on a procedure, by which MN10 quicklyacquires the external transmission address relating to the subnet 30after the handover on a link of the subnet 30 connected after thehandover.

1st Embodiment

First, description will be given on the first embodiment of the presentinvention. FIG. 2 is a sequence chart to show principal processingcommon to the first to the fourth embodiments of the present invention.The sequence chart given in FIG. 2 shows only the principal processingaccording to the present invention, and the technique explained in thefirst to the fourth embodiments of the present invention can be carriedout in combination with a first or a second operation mode in FMIP shownin FIG. 41 and FIG. 42.

In the sequence chart shown in FIG. 2, similarly to the conventionalFMIP shown in FIG. 41 and FIG. 42, MN10 is first connected to the subnet20 (Step S101), and under this connected condition, AP32 within therange of a new subnet 30 is discovered, and the execution of L2 handoverto AP32 is decided (S103). Then, MN10 transmits information that theexternal transmission address is requested in addition to RtSolPrmessage including AP-ID of AP32 (Step S105).

PAR21 receives RtSolPr message from MN10, and, by using the procedure asa procedure to acquire information of NAR31 as executed in theconventional FMIP technique, for instance, it acquires the externaltransmission address relating to the subnet 30 (Step S107). Moreconcretely, PAR21 retrieves an access router present in the neighborhoodaccording to AP-ID of AP32 included in the RtSolPr message and acquiresa link local address of NAR31 belonging to the subnet 30 or a defaultrouter 37. Or, PAR21 can acquire a link local address of NAR31 belongingto the subnet 30 or the default router 37 from information alreadyretrieved (the information retained by PAR21).

Then, PAR21 notifies the external transmission address relating to thesubnet 30 acquired in Step S107 to MN10 at the time of transmission ofPrRtAdv message including information of NAR31 (Step S109). In so doing,MN10 can acquire the external transmission address relating to thesubnet 30 from PAR21. Specifically, MN10 can quickly execute packettransmission to outside (e.g. CN40) in the subnet 30 by setting up alink local address of NAR31 as acquired in advance by the aboveprocedure or a link local address of the default router 37 immediatelyafter the handover to the link of the subnet 30 (Step S111) as a defaultrouter in a routing table.

FIG. 3 is a block diagram to show an example of arrangement of PAR inthe first embodiment of the present invention. In FIG. 3, functions ofPAR21 are shown by blocks, while these functions can be fulfilled byhardware and/or software. PAR21 shown in FIG. 3 comprises receivingmeans 1101, transmitting means 1102, RtSolPr processing means 1103,PrRtAdv generating means 1104, neighbor subnet information acquiringmeans 1105, and neighbor subnet information storing means 1106.

The receiving means 1101 and the transmitting means 1102 are the meansfor transmitting and receiving packet by connecting with AP (AP22 andAP23) present under the control or connecting with IP network 15.Normally, these are different from an interface to be connected to AP22and AP23 or an interface to be connected with IP network 15, and aplurality of receiving means and transmitting means are provided.However, these are shown here as a single receiving means 1101 and asingle transmitting means 1102.

Also, the RtSolPr processing means 1003 carries out processing relatingto RtSolPr message received from MN10 and instructs the PrRtAdvgenerating means 1104 to generate PrRtAdv message, which is to be aresponse message, and it also instructs the neighbor subnet informationacquiring means 1105 to acquire the external transmission addressrelating to the subnet 30 of handover destination of MN10.

When receiving an instruction from the RtSolPr processing means 1103,PrRtAdv generating means 1104 generates a PrRtAdv message including theexternal transmission address relating to the subnet 30 notified by theneighbor subnet information acquiring means 1105.

The neighbor subnet information acquiring means 1105 is the means toacquire the external transmission address relating to the subnet 30 andto notify the external transmission address relating to the subnet 30 asacquired to the PrRtAdv generating means 1104. For instance, theneighbor subnet information acquiring means 1105 transmits informationto request the external transmission address relating to the subnet 30to NAR31 or to the server as necessary via the transmitting means 1102and receives the external transmission address relating to the subnet 30via the receiving means 1101 and can acquire the external transmissionaddress relating to the subnet 30. Also, it is possible to store theexternal transmission address relating to the subnet 30 as acquired inthe neighbor subnet information storing means 1106. It is also possibleto acquire the external transmission address relating to the subnet 30as desired by referring to the external transmission address relating tothe subnet 30 stored in the neighbor subnet information storing means1106.

FIG. 4A represents diagrams to show the request information of theexternal transmission address from MN to be processed in PAR shown inFIG. 3, and FIG. 4B is a diagram to show an example of data arrangementof the notifying information of the external transmission address to betransmitted to MN. As shown in FIG. 4A, from MN10, PAR21 receives aconventional RtSolPr message or an RtSolPr message added withinformation to instruct the request of the external transmissionaddress.

For example, PAR21 is so arranged that it transmits the PrRtAdv messageincluding the external transmission address shown in FIG. 4B in case aconventional RtSolPr message has been received (i.e. the conventionalRtSolPr message plays a role of information to request the externaltransmission address). Or, PAR21 is so arranged that it verifies whetherthe information to instruct the request of the external transmissionaddress is present or not within the RtSolPr message and transmits thePrRtAdv message including the external transmission address shown inFIG. 4B in case the information to instruct the request of the externaltransmission address is added.

Therefore, although not shown in the figures, for the purpose ofachieving the first embodiment of the present invention, MN10 must havethe means to extract the external transmission address from within thePrRtAdv message received from PAR21. In case PAR21 is so arranged thatit transmits the PrRtAdv message including the external transmissionaddress to MN10, which transmits the RtSolPr message added with theinformation to instruct the request of the external transmissionaddress, MN10 must have the means to insert the information to instructthe request of the external transmission address within the RtSolPrmessage.

As described in the above, according to the first embodiment of thepresent invention, when MN10 executes the handover to different subnets30, MN10 requests the external transmission address relating to thesubnet 30 by transmitting RtSolPr message to PAR21 connected before thehandover, and PAR21 can notify the external transmission addressrelating to the subnet 30 by transmitting the PrRtAdv message, which isa response message. Thus, MN10 can acquire the external transmissionaddress relating to the subnet 30 connected after the handover on a linkof the subnet 20 connected before the handover and can quickly transmitpacket to outside immediately after the handover.

In the first embodiment as described above, explanation has been givenon a case where it is so arranged that the external transmission addressis included in the PrRtAdv message, which is a response message toRtSolPr message received from MN10, and PAR21 transmits the PrRtAdvmessage including the external transmission address. However, PAR21 canalso transmit the PrRtAdv message (unsolicited PrRtAdv message) withoutreceiving the RtSolPr message from MN10 (See Section 3.3 of theNon-Patent Document 1).

In the unsolicited PrRtAdv message transmitted under the condition wherethere is no request by the RtSolPr message, information relating to aspecific subnet among the subnets in the neighborhood (e.g. informationsuch as IP address of NAR31 belonging to the subnet or a network prefixof the subnet) is included. Upon receipt of the unsolicited PrRtAdvmessage, MN10 must execute the handover to the specific subnet includedin the unsolicited PrRtAdv message. That is, the unsolicited PrRtAdvmessage is a message, which includes the information relating to aspecific subnet and to instruct the specific subnet to carry out thehandover.

As shown in FIG. 4B, according to the present invention, it can also beso arranged that the external transmission address relating to aspecific subnet is included in the unsolicited PrRtAdv message asdescribed above together with the information relating to the specificsubnet, and that PAR 21 can transmit the unsolicited PrRtAdv messageincluding the external transmission address to MN10 under the conditionthat there is no request from MN10.

2nd Embodiment

Next, description will be given on the second embodiment of the presentinvention. The operation in the second embodiment of the invention isthe same as the operation described in the above in connection with thesequence chart of FIG. 2, and detailed description is not given here.

FIG. 5 is a block diagram to show an example of arrangement of PAR inthe second embodiment of the present invention. Although the functionsof PAR 21 are shown by blocks in FIG. 5, these functions can befulfilled by hardware and/or software. PAR21 shown in FIG. 5 comprisesreceiving means 1201, transmitting means 1202, RtSolPr processing means1203, PrRtAdv generating means 1204, neighbor subnet informationacquiring means 1205, neighbor subnet information storing means 1206,and external transmission address notifying message generating means1207. The receiving means 1201, the transmitting means 1202, the RtSolPrprocessing means 1203, and the neighbor subnet information storing means1206 are the same as the receiving means 1101, the transmitting means1102, the RtSolPr processing means 1103, and the neighbor subnetinformation storing means 1106 as shown in FIG. 3 respectively.

The PrRtAdv generating means 1204 is the means to generate the samemessage as the PrRtAdv message generated in the conventional FMIP uponreceipt of an instruction from the RtSolPr processing means 1203. Thatis, it is the same as the means to generate the PrRtAdv message in theconventional FMIP.

The neighbor subnet information acquiring means 1205 is the means toacquire the external transmission address relating to the subnet 30 andto notify the external transmission address relating to the subnet 30 asacquired to the external transmission address notifying messagegenerating means 1207. It is different from the neighbor subnetinformation acquiring means 1105 as shown in FIG. 3 in that thenotifying destination of the external transmission address relating tothe subnet 30 is the external transmission address notifying messagegenerating means 1207, and the other functions are the same as those ofthe neighbor subnet information acquiring means 1105 as shown in FIG. 3.

The external transmission address notifying message generating means1207 is the means to generate an external transmission address notifyingmessage including the external transmission address relating to thesubnet 30 notified from the neighbor subnet information acquiring means1205. The external transmission address notifying message is differentfrom the PrRtAdv message.

FIG. 6A represents diagrams to show the information to request theexternal transmission address from MN to be processed in PAR shown inFIG. 5. FIG. 6B represents diagrams to show an example of dataarrangement of the information to notify the external transmissionaddress transmitted to MN. The RtSolPr message shown in FIG. 6A is thesame as the message shown in FIG. 4A.

It is so arranged that, besides the PrRtAdv message, PAR21 transmits theexternal transmission address notifying message to MN10 when theconventional RtSolPr message shown in FIG. 6A or the RtSolPr messageincluding the request of the external transmission address has beenreceived. The external transmission address notifying message must betransmitted to MN10 before MN10 executes L2 handover. The externaltransmission address notifying message and the PrRtAdv message aretransferred by packets independent from each other, and the externaltransmission address notifying message can be transmitted at any timingas desired without depending on the timing to transmit the PrRtAdvmessage. It is also possible to synchronize the transmission of theexternal transmission address notifying message with the transmission ofthe PrRtAdv message and to arrange that both messages, i.e. the externaltransmission address notifying message and the PrRtAdv message, can becontinuously transmitted from PAR21 to MN10, for instance.

Although not shown in the figures, for the purpose of achieving thesecond embodiment of the present invention, MN21 must have the means toextract the external transmission address from the external transmissionaddress notifying message received from PAR21 (e.g. the externaltransmission address notifying message processing means 1417 shown inFIG. 11 as to be given later). In case it is so arranged that PAR21transmits the PrRtAdv message including the external transmissionaddress to MN10, which has sent the RtSolPr message added with theinformation to instruct the request of the external transmissionaddress, MN10 must have the means to insert the information to instructthe request of the external transmission address in the RtSolPr messagealthough not shown in the figures.

As described above, according to the second embodiment of the presentinvention, when MN10 carries out the handover to different subnets 30,MN10 can request the external transmission address relating to thesubnet 30 by transmitting the RtSolPr message to PAR21 connected beforethe handover. PAR21 can notify the external transmission addressrelating to the subnet 30 by transmitting the external transmissionaddress notifying message different from the PrRtAdv message, which is aresponse message. MN10 can acquire the external transmission addressrelating to the subnet connected after the handover on a link of thesubnet 20 connected before the handover and can quickly transmit packetto outside immediately after the handover.

3rd Embodiment

Next, description will be given on the third embodiment of the presentinvention. The operation in the third embodiment of the invention is thesame as the operation explained in the above by referring to thesequence chart of FIG. 2, and detailed description is not given here.

FIG. 7 is a block diagram to show an example of arrangement of PAR inthe third embodiment of the present invention. Although the functions ofPAR21 are shown by blocks in FIG. 7, these functions can be fulfilled byhardware and/or software. PAR21 shown in FIG. 7 comprises receivingmeans 1301, transmitting means 1302, RtSolPr processing means 1303,PrRtAdv generating means 1304, neighbor subnet information acquiringmeans 1305, neighbor subnet information storing means 1306, and externaltransmission address requesting message processing means 1307. Thereceiving means 1301, the transmitting means 1302, the PrRtAdvgenerating means 1304, and the neighbor subnet information storing means1306 are the same as the receiving means 1101, the transmitting means1102, the PrRtAdv generating means 1104, and the neighbor subnetinformation storing means 1106 as shown in FIG. 3 respectively.

The RtSolPr processing means 1303 is the means to carry out processingrelating to the RtSolPr message received from MN10 and to instructgeneration of the PrRtAdv message, which is to be a response message, tothe PrRtAdv generating means 1304. That is, it is the same as the meansto perform processing of the RtSolPr message in the conventional FMIP.

The neighbor subnet information acquiring means 1305 is the means toreceive and instruct to acquire the external transmission addressrelating to the subnet 30 from the external transmission addressrequesting message processing means 1307 and to acquire the externaltransmission address relating to the subnet 30 and to notify theexternal transmission address relating to the subnet 30 as acquired tothe PrRtAdv generating means 1304. It is different from the neighborsubnet information acquiring means 1105 shown in FIG. 3 in that theinstruction to acquire the external transmission address relating to thesubnet 30 is given from the external transmission address requestingmessage processing means 1307, and the other functions are the same asthose of the neighbor subnet information acquiring means 1105 as shownin FIG. 3.

The external transmission address requesting message processing means1307 is the means to perform processing relating to the externaltransmission address requesting message transmitted at the same timingas the RtSolPr message by MN10 and to instruct the acquisition of theexternal transmission address relating to the subnet specified by thismessage to the neighbor subnet information acquiring means 1305. It isdesirable that an arbitrary information able to specify the subnet 30such as AP-ID of AP32 or component element of the subnet is included inthe external transmission address requesting message.

FIG. 8A represents diagrams to show the request information of theexternal transmission address from MN as to be processed in PAR shown inFIG. 7. FIG. 8B is a diagram to show an example of data arrangement ofthe notifying information of the external transmission address to betransmitted to MN. The PrRtAdv message shown in FIG. 8B is the same asthe one shown in FIG. 4B.

PAR21 is so arranged that it transmits the PrRtAdv message including theexternal transmission address indicated in FIG. 8B when the externaltransmission address requesting message transmitted at the same timingas the RtSolPr message by MN10 is received (i.e. PAR21 receives both theRtSolPr message and the external transmission address requestingmessage). Here, description has been given on the case where theexternal transmission address requesting message is transmitted at thesame timing as the RtSolPr message, while it can also be so arrangedthat PAR21 receives the external transmission address requesting messageearlier than the RtSolPr message and prepares for the notification ofthe external transmission address relating to the subnet 30 in advanceto MN10 and the PrRtAdv message including the external transmissionaddress can be quickly generated in case the RtSolPr message is receivedthereafter.

Although not shown in the figures, for the purpose of achieving thethird embodiment of the present invention, MN10 must have the means togenerate the external transmission address requesting message at thesame time as the generation of the RtSolPr message after deciding theexecution of the handover (e.g. the external transmission addressrequesting message generating means 1416 shown in FIG. 11 as to be givenlater) and also must have the means to extract the external transmissionaddress from the PrRtAdv message received from PAR21.

As described above, according to the third embodiment of the presentinvention, MN10 can request the external transmission address relatingto the subnet 30 by transmitting the external transmission addressrequesting message to PAR21 connected before the handover and PAR21 cannotify the external transmission address relating to the subnet 30 asacquired according to the external transmission address requestingmessage by transmitting the PrRtAdv message. MN10 can acquire theexternal transmission address relating to the subnet connected after thehandover on a link of the subnet 20 connected before the handover andcan quickly transmit packet to outside immediately after the handover.

4th Embodiment

Next, description will be given on the fourth embodiment of the presentinvention. The operation in the fourth embodiment of the invention isthe same as the operation explained above in connection with thesequence chart of FIG. 2, and detailed description is not given here.

FIG. 9 is a block diagram to show an example of arrangement of PAR inthe fourth embodiment of the present invention. Although the functionsof PAR21 are shown by blocks in FIG. 9, these functions can be fulfilledby hardware and/or software. PAR21 shown in FIG. 9 comprises receivingmeans 1401, transmitting means 1402, RtSolPr processing means 1403,PrRtAdv generating means 1404, neighbor subnet information acquiringmeans 1405, neighbor subnet information storing means 1406, externaltransmission address requesting message processing means 1407, andexternal transmission address notifying message generating means 1408.The receiving means 1401, the transmitting means 1402, and the neighborsubnet information storing means 1406 are the same as the receivingmeans 1101, the transmitting means 1102, and the neighbor subnetinformation storing means 1106 as shown in FIG. 3 respectively. ThePrRtAdv generating means 1404 and the external transmission addressnotifying message generating means 1408 are the same as the PrRtAdvgenerating means 1204 and the external transmission address notifyingmessage generating means 1207 as shown in FIG. 5. The RtSolPr processingmeans 1403 and the external transmission address requesting messageprocessing means 1407 are the same as the RtSolPr processing means 1303and the external transmission address requesting message processingmeans 1307 as shown in FIG. 7.

The neighbor subnet information acquiring means 1405 is the means toacquire the external transmission address relating to the subnet 30 byreceiving an instruction to acquire the external transmission addressrelating to the subnet 30 from the external transmission addressrequesting message processing means 1407 and to notify the externaltransmission address relating to the subnet 30 as acquired to theexternal transmission address notifying message generating means 1408.The neighbor subnet information acquiring means 1405 has the samefunction as that of the neighbor subnet information acquiring means 1105as shown in FIG. 3, and detailed description is not given here.

FIG. 10A represents diagrams to show the request information of theexternal transmission address from MN to be processed in PAR shown inFIG. 9. FIG. 10B represents diagrams to show an example of dataarrangement of the external transmission address transmitted to MN. Thepacket transmitted to PAR21 from MN10 as shown in FIG. 10A is the sameas the one shown in FIG. 8A, and the packet transmitted to MN10 fromPAR21 shown in FIG. 10B is the same as the one shown in FIG. 6B.

FIG. 11 is a block diagram to show an example of arrangement of MN inthe fourth embodiment of the present invention. Although the functionsof MN10 are shown by blocks in FIG. 11, these functions can be fulfilledby hardware and/or software. MN10 shown in FIG. 11 comprises radioreceiving means 1411, radio transmitting means 1412, L2 handoverdetermining means 1413, RtSolPr generating means 1414, PrRtAdvprocessing means 1415, external transmission address requesting messagegenerating means 1416, and external transmission address notifyingmessage processing means 1417.

The radio receiving means 1411 and the radio transmitting means 1412 arethe means to perform radio communication with APs (AP22, AP23, AP32 andAP33) and to perform communication with PAR21 and NAR31 at superiorpositions and with arbitrary node connected to the IP network 15. The L2handover determining means 1413 is the means to determine the executionof the handover to optimal AP (here, AP32 because it is assumed that MNperforms the handover from AP23 to AP32) by judging the intensity ofelectric field issued from each of the APs.

The RtSolPr generating means 1414 is the means to generate the RtSolPrmessage including a link layer address of AP32 before performing thehandover upon receipt of an instruction to execute the handover from L2handover determining means 1413. It is also the means to include thelink layer address of AP32 at the handover destination and to instructthe generation of a message to request the external transmission addressrelating to the subnet 30 at the handover destination (externaltransmission address requesting message) to the external transmissionaddress requesting message generating means 1416. The externaltransmission address requesting message generating means 1416 is themeans to generate an external transmission address requesting message byreceiving an instruction to generate the external transmission addressrequesting message from the RtSolPr generating means 1414 (or aninstruction to execute the handover to be sent from the L2 handoverdetermining means 1413).

Both of the RtSolPr message in the RtSolPr generating means 1414 and theexternal transmission address requesting message in the externaltransmission address requesting message generating means 1416 aregenerated with the decision of the handover by the L2 handoverdetermining means 1413 as trigger. The RtSolPr message and the externaltransmission address requesting message are transmitted to PAR21 fromMN10, each as different packet, as shown in FIG. 10A.

The PrRtAdv processing means 1415 is the means to perform processing ofthe PrRtAdv message received from PAR21. That is, this is the same asthe means to process the PrRtAdv message in the conventional FMIP. Theexternal transmission address notifying message processing means 1417 isthe means to perform processing of the external transmission addressnotifying message received from PAR21 and to extract an externaltransmission address relating to the subnet 30 among the externaltransmission address notifying message. After being processed by routesetting means (not shown) 1417, the external transmission addressprocessed by the external transmission address notifying messageprocessing means 1417 is described in a setting column of a link localaddress as required within the default router list.

As described above, according to the fourth embodiment of the presentinvention, when MN10 performs the handover to different subnets 30, MN10requests the external transmission address relating to the subnet 30 bytransmitting the external transmission address requesting message toPAR21 connected before the handover, and PAR21 can notify the externaltransmission address relating to the subnet 30 acquired according to theexternal transmission address requesting message by transmitting theexternal transmission address notifying message. MN10 can acquire theexternal transmission address relating to the subnet 30 connected afterthe handover and can quickly transmit packet to outside immediatelyafter the handover.

In the first to the fourth embodiment as given above, description hasbeen given on 4 types of aspects to request the external transmissionaddress relating to the subnet 30 to PAR21 by taking opportunity of thegeneration of the RtSolPr message (decision of the execution of thehandover). In the fifth to the eighth embodiments as given below,description will be given on 4 types of aspects, in which the externaltransmission address relating to the subnet 30 is requested to PAR21 bytaking opportunity of the generation of an FBU message (or the receivingof the PrRtAdv message).

5th Embodiment

Next, description will be given on the fifth embodiment of the presentinvention. FIG. 12 is a sequence chart to show principal processingcommon to the fifth to the eighth embodiments of the present invention.The sequence chart of FIG. 12 shows only the principal processingaccording to the present invention. The technique explained in the fifthto the eighth embodiments of the present invention can be carried out incombination with a first operation mode in FMIP as shown in FIG. 41(operation mode when MN10 transmits the FBU message on a link before thehandover).

In the sequence chart shown in FIG. 12, similarly to the prior art asshown in FIG. 41, MN10 first makes connection with the subnet 20 (StepS201). Under the connected condition, AP32 under the control of a newsubnet 30 is discovered, and the execution of L2 handover to AP32 isdetermined (Step S203). Then, MN10 transmits the RtSolPr messageincluding AP-ID of AP32 (Step S205). By receiving the PrRtAdv messagefrom PAR21 (Step S207), it is possible to generate NCoA adaptable at thesubnet 30 of the handover destination.

In addition to the FBU message including NCoA as given above, MN10transmits information to request the external transmission address (StepS209). After receiving the FBU message, PAR21 retrieves access routerpresent in the neighborhood as explained in the first to the fourthembodiments and acquires a link local address of NAR31 belonging to thesubnet 30 or of a default router 37, or acquires a link local address ofNAR31 belonging to the subnet 30 or of a default router 37 from theinformation already retrieved (information retained by PAR21), oracquires a link local address of NAR31 belonging to the subnet 30 or ofthe default router 37 (external transmission address by using otherprocedure (more concretely, the procedure to be explained in the ninthto the twelfth embodiments later) (Step S211).

Then, PAR21 notifies the external transmission address relating to thesubnet 30 acquired in Step S211 to MN10 at the timing to transmit FBAckmessage including the information of NAR31 (Step S213). In so doing,MN10 can acquire the external transmission address relating to thesubnet 30 from PAR21. Specifically, MN10 can quickly execute packettransmission to outside (e.g. CN40) in the subnet 30 by setting up thelink local address of NAR31 acquired in advance by the procedure givenabove or the link local address of the default router 37 as defaultrouter immediately after the handover to the link of the subnet 30 (StepS215).

FIG. 13 is a block diagram to show an example of arrangement of PAR inthe fifth embodiment of the present invention. Although the functions ofPAR21 are shown by blocks in FIG. 13, these functions can be fulfilledby hardware and/or software. PAR21 shown in FIG. 13 comprises receivingmeans 2101, transmitting means 2102, FBU processing means 2103, FBAckgenerating means 2104, neighbor subnet information acquiring means 2105,and neighbor subnet information storing means 2106. PAR21 is providedwith various types of functions: a function as the RtSolPr processingmeans to perform processing on the RtSolPr message received from MN10, afunction as the PrRtAdv generating means to generate the PrRtAdv messagetransmitted to MN10, a function as HI processing means to generate HImessage transmitted to NAR31, and a function as HAck processing means toprocess HAck message received from NAR31, etc. However, detaileddescription and illustrations are not given here.

PAR21 as shown in FIG. 13 may be explained as the replacement of PAR21shown in FIG. 3, i.e. by replacing the RtSolPr processing means 1103with the FBU processing means 2103 and also as the replacement of PAR21shown in FIG. 3, i.e. by replacing the PrRtAdv generating means 1104with the FBAck generating means 2104. Specifically, as shown in FIG.14A, PAR21 receives the conventional FBU message or the FBU messageadded with information to instruct the request of the externaltransmission address.

For example, PAR21 may be so arranged that it receives FBAck messageincluding the external transmission address as shown in FIG. 14B whenthe conventional type FBU message is received (i.e. the conventional FBUmessage plays a role as information to request the external transmissionaddress). Or, PAR21 is so arranged that it transmits FBAck messageincluding the external transmission address shown in FIG. 14B in casethe information to instruct the request of the external transmissionaddress is added by verifying whether the information to instruct therequest of the external transmission address defined within FBU messageis present or not.

Although not shown in the figures, for the purpose of achieving thefifth embodiment of the invention, MN10 must have the means to extractthe external transmission address from the FBAck message received fromPAR21. In case PAR21 is so arranged that it transmits FBAck messageincluding the external transmission address to MN10, which has sent theFBU message added with the information to instruct the request of theexternal transmission address, MN10 must have the means to insert theinformation to instruct the request of the external transmission addressin the FBU message, although not shown in the figures.

As described above, according to the fifth embodiment of the presentinvention, when MN10 executes the handover to different subnets 30, MN10can request the external transmission address relating to the subnet 30by transmitting the FBU message to PAR21 connected before the handover,and PAR21 can notify the external transmission address relating to thesubnet 30 by transmitting the FBAck message, which is a responsemessage. MN10 can acquire the external transmission address relating tothe subnet 30 connected after the handover and can quickly performpacket transmission to outside immediately after the handover.

6th Embodiment

Next, description will be given on the sixth embodiment of the presentinvention. The sixth embodiment of the present invention has a matchingrelation with the second embodiment as described above. This matchingrelation is the same as the matching relation between the firstembodiment and the fifth embodiment. Specifically, PAR21 as shown inFIG. 15 gives the instruction to generate FBAck to the FBAck generatingmeans 2204. The FBU processing means 2203 instructs the generation ofFBAck to the FBAck generating means 2204 when the FBU message isreceived. It requests the acquisition of the external transmissionaddress relating to the subnet 30 to the neighbor subnet informationacquiring means 2205. The neighbor subnet information acquiring means2205 supplies the acquired external transmission address to the externaltransmission address notifying message generating means 2207, and it isso arranged that the external transmission address notifying message isgenerated in addition to the FBAck message at the external transmissionaddress notifying message generating means 2207.

Specifically, PAR21 is so arranged that it transmits the FBAck messageand the external transmission address notifying message to MN10 as shownin FIG. 16B when the conventional FBU message shown in FIG. 16A or theFBU message including the request of the external transmission addressis received. Except that there is a difference between the RtSolPrmessage and the FBU message and a difference between the PrRtAdv messageand the FBAck message, the details of data processing and the details ofthe data arrangement in the sixth embodiment of the present invention aswell as the arrangement necessary in MN10 are the same as in the secondembodiment as given above.

As described above, according to the sixth embodiment of the presentinvention, when MN10 executes the handover to different subnets 30, MN10requests the external transmission address relating to the subnet 30 bytransmitting the FBU message to PAR21 connected before the handover, andPAR21 can notify the external transmission address relating to thesubnet 30 by transmitting the external transmission address notifyingmessage different from the FBAck message, which is a response message.MN10 can acquire the external transmission address relating to thesubnet 30 connected after the handover on a link of the subnet 20connected before the handover and can quickly execute packettransmission to outside immediately after the handover.

7th Embodiment

Next, description will be given on the seventh embodiment of the presentinvention. The seventh embodiment of the present invention has amatching relation with the third embodiment as described above, and thismatching relation is the same as the matching relation of the firstembodiment with the fifth embodiment. That is, when PAR21 as shown inFIG. 17 receives the FBU message and the external transmission addressrequesting message, the FBU generating means 2303 instructs thegeneration of FBAck to the FBAck generating means 2304, and the externaltransmission address requesting message processing means 2307 requeststhe acquisition of the external transmission address relating to thesubnet 30 to the neighbor subnet information acquiring means 2305. Theneighbor subnet information acquiring means 2305 supplies the externaltransmission address as acquired to the FBAck generating means 2304, andthe FBAck message including the external transmission address isgenerated.

Specifically, when PAR21 receives the conventional FBU message as shownin FIG. 18A and the external transmission address requesting message, itis so arranged that it transmits an FBAck message including the externaltransmission address to MN10 as shown in FIG. 18B. Except that there isa difference between the RtSolPr message and the FBU message and adifference between the PrRtAdv message and the FBAck message, thedetails of data arrangement and the details of data processing in theseventh embodiment of the present invention as well as the arrangementnecessary in MN10 are the same as those of the third embodiment asdescribed above.

As described above, according to the seventh embodiment of the presentinvention, when MN10 executes the handover to different subnets 30, MN10requests the external transmission address relating to the subnet 30 bytransmitting the external transmission address requesting message to PAR21 connected before the handover, and PAR21 can notify the externaltransmission address relating to the subnet 30 acquired according to theexternal transmission address requesting message by transmitting theFBAck message. MN10 can acquire the external transmission addressrelating to the subnet 30 connected after the handover and can quicklyexecute packet transmission to outside immediately after the handover.

8th Embodiment

Next, description will be given on the eight embodiment of the presentinvention. The eighth embodiment of the present invention has a matchingrelation with the fourth embodiment as described above, and thismatching relation is the same as the matching relation of the firstembodiment with the fifth embodiment. Specifically, when PAR21 shown inFIG. 19 receives the FBU message and the external transmission addressrequesting message, the FBU processing means 2403 instructs thegeneration of FBAck to the FBAck generating means 2404. The externaltransmission address requesting message processing means 2407 requeststhe acquisition of the external transmission address relating to thesubnet 30 to the neighbor subnet information acquiring means 2405. It isso arranged that the neighbor subnet information acquiring means 2405supplies the external transmission address as acquired to the externaltransmission address notifying message generating means 2408 so that theexternal transmission address notifying message is generated, inaddition to the FBAck message, at the external transmission addressnotifying message generating means 2408.

Specifically, when PAR21 receives the conventional FBU message as shownin FIG. 20A and the external transmission address requesting message, itis so arranged that PAR21 transmits the FBAck message and the externaltransmission address notifying message to MN10 as shown in FIG. 20B.Except that there is a difference between the RtSolPr message and theFBU message and there is a difference between the PrRtAdv message andthe FBAck message, the details of data arrangement and the details ofdata processing in the eighth embodiment of the present invention aswell as the arrangement necessary in MN10 are the same as those of thefourth embodiment as given above.

As described above, according to the eighth embodiment of the presentinvention, when MN10 executes the handover to different subnets 30, MN10requests the external transmission address relating to the subnet 30 bytransmitting the external transmission address requesting message toPAR21 connected before the handover, and PAR21 can notify the externaltransmission address relating to the subnet 30 acquired according to theexternal transmission address requesting message by transmitting theexternal transmission address notifying message. MN10 can acquire theexternal transmission address relating to the subnet 30 connected afterthe handover and can quickly execute packet transmission to outsideimmediately after the handover.

Also, it can be so arranged that, by combining the first to the fourthembodiments as given above with the fifth to the eighth embodiments,PAR21 can notify the external transmission address relating to thesubnet 30 as requested from MN10 to MN10 when the RtSolPr message isreceived.

In the fifth to the eighth embodiments as given above, description hasbeen given on 4 types of aspects to request the external transmissionaddress relating to the subnet 30 to PAR21 by taking opportunity of thegeneration of the FBU message (or the receiving of the PrRtAdv message).In the fifth to eighth embodiments, there is no special restriction onthe procedure to acquire the external transmission address relating tothe subnet 30 at each of the neighbor subnet information acquiring means2105, 2205, 2305 and 2405 of PAR21. In the ninth to the twelfthembodiments as given below, description will be given on the procedure,in which the procedure to acquire the external transmission addressrelating to the subnet 30 at each of the neighbor subnet informationacquiring means 2105, 2205, 2305, and 2405 in the fifth to the eighthembodiments is carried out in association with transmitting andreceiving of the HI message and the HAck message between PAR21 and NAR31as defined in the conventional FMIP.

9th Embodiment

Next, description will be given on the ninth embodiment of the presentinvention. FIG. 21 is a sequence chart to show principal processingcommon to the ninth to the twelfth embodiments of the present invention.In the sequence chart of FIG. 21, only the principal processingaccording to the present invention is shown. The technique to beexplained in connection with the ninth to the twelfth embodiments of thepresent invention can be carried out in combination with the case wherethe HI message and the HAck message are given and taken between PAR21and NAR31 in the first operation mode in FMIP as shown in FIG. 41 (theoperation mode in the case where MN10 transmits the FBU message on alink before the handover).

The sequence chart shown in FIG. 21 is basically the same as thesequence chart shown in FIG. 12. However, in contrast to the sequencechart of FIG. 12 where there is no special restriction on the externaltransmission address relating to the subnet in Step S211, in thesequence chart of FIG. 21, PAR21 requests the external transmissionaddress to NAR31 at the time of transmitting of the HI message to NAR31(Step S311), and NAR31 notifies the external transmission address toPAR21 when transmitting the HAck message, which is a response of the HImessage (Step S313).

Then, PAR2 notifies the external transmission address relating to thesubnet 30 to MN10 at the time of transmission of the FBAck messageincluding the information of NAR31 (Step S317). As a result, MN10 canacquire the external transmission address relating to the subnet 30 fromPAR21. That is, immediately after executing the handover to the link ofthe subnet 30 (Step S319), MN10 can set up a link local address of NAR31acquired in advance by the procedure as given above or a link localaddress of a default router 37 to the transmission packet and canquickly execute packet transmission to outside (e.g. to CN40) in thesubnet 30.

FIG. 22 is a block diagram to show an example of arrangement of PAR inthe ninth embodiment of the present invention. Although the functions ofPAR21 are shown by blocks in FIG. 22, these functions can be fulfilledby hardware and/or software. PAR21 shown in FIG. 22 comprises receivingmeans 3101, transmitting means 3102, FBU processing means 3103, FBAckgenerating means 3104, and neighbor information acquiring means 3105.The neighbor subnet information acquiring means 3105 has HI generatingmeans 3106 to generate the HI message and HAck processing means 3107 toperform processing of the HAck message.

PAR21 as explained in the ninth embodiment of the present inventiontransmits and receives the HI message and the HAck message when arequest of the external transmission address is received by the FBUmessage from MN10. Then, it acquires the external transmission addressrelating to the subnet 30, which is the handover destination of MN10, byutilizing the transmitting and the receiving of the HI message and theHAck message and transmits the FBAck message including the externaltransmission address to MN10. Therefore, PAR21 as explained in the ninthembodiment of the present invention may be regarded as an aspect ofPAR21 as explained in the fifth embodiment. In particular, it is soarranged that the HI message and the HAck message can be used withregard to the function of the neighbor subnet information acquiringmeans 2105 as shown in FIG. 13.

Description will be given below on the arrangement of PAR21 shown inFIG. 22 by comparing with the arrangement of PAR21 shown in FIG. 13.PAR21 shown in FIG. 22 comprises receiving means 3101, transmittingmeans 3102, FBU processing means 3103, and FBAck generating means 3104,and these are basically the same as the receiving means 2101, thetransmitting means 2102, the FBU processing means 2103, and the FBAckgenerating means 2104 shown in FIG. 13.

The HI generating means 3106 of PAR21 shown in FIG. 22 is the means togenerate HI message in the conventional FMIP or HI message including therequest of the external transmission address. The generation of the HImessage by the HI generating means 3106 is carried out at theinstruction to generate the HI message as supplied from the FBUprocessing means 3103. The HI message generated by the HI generatingmeans 3106 is transmitted to NAR31 via the transmitting means 3102. FromNAR31, the HAck message including the external transmission addressrelating to the subnet 30 is received. Processing of the HAck message isperformed by the HAck processing means 3107. From the HAck processingmeans 3107, an instruction to generate FBAck is sent to the FBAckgenerating means 3104 together with the external transmission addressrelating to the subnet 30 extracted from the HAck message. As a result,the FBAck generating means 3104 can generate the FBAck message includingthe external transmission address of the subnet 30.

FIG. 23 is a block diagram to show an example of arrangement of NAR inthe ninth embodiment of the present invention. Although the functions ofNAR31 are shown by blocks in FIG. 23, these functions can be fulfilledby hardware and/or software. NAR23 shown in FIG. 23 comprises receivingmeans 3111, transmitting means 3112, HI processing means 3113, HAckgenerating means 3114, subnet information acquiring means 3115, andsubnet information storing means 3116.

When an HI message is received from PAR21, NAR31 shown in FIG. 23performs processing by HI processing means 3113 (such as verificationprocessing of NCoA) and gives an instruction to generate HAck message tothe HAck generating means 3114, and requests the acquisition of theexternal transmission address relating to the subnet (NAR31's ownsubnet) to the subnet information acquiring means 3115. The subnetinformation acquiring means 3115 reads its own link local address in thesubnet 30 or a link local address of the default router 37 from thesubnet information storing means 3116 or performs communication withother route in the subnet 30 and acquires the link local address of thedefault router 37 in the subnet 30, and the results of the acquisitionare notified to the HAck generating means 3114. As a result, the HAckgenerating means 3114 can generate the HAck message including theexternal transmission address relating to the subnet 30.

FIG. 24A represents diagrams to show request information of the externaltransmission address to be given and taken between PAR shown in FIG. 22and NAR shown in FIG. 23. FIG. 24B is a diagram to show an example ofdata arrangement of the notifying information of the externaltransmission address. It is so arranged that PAR21 transmits the HImessage in the conventional FMIP as shown in FIG. 24A (in this case, theconventional HI message plays a role of information to request theexternal transmission address) or it transmits the HI message includingthe request of the external transmission address. Upon receipt of the HImessage, NAR31 transmits the HAck message including the externaltransmission address as shown in FIG. 24B.

As described above, according to the ninth embodiment of the presentinvention, when MN10 executes the handover to different subnets 30, whenreceiving the external transmission address relating to the subnet 30from MN10, PAR21 requests the external transmission address relating tothe subnet 30. NAR31 can notify the external transmission addressrelating to the subnet 30 by transmitting an HAck message, which is itsresponse message. PAR21 notifies the external transmission addressrelating to the subnet 30 as acquired to MN10. Then, MN10 can acquirethe external transmission address relating to the subnet 30 connectedafter the handover and can quickly execute packet transmission tooutside immediately after the handover.

It has been already described that, in PAR21 shown in FIG. 22, theneighbor subnet information acquiring means 2105 in PAR21 in the fifthembodiment (PAR21 shown in FIG. 13) can acquire the externaltransmission address relating to the subnet 30 at the time oftransmitting and receiving of the HI message and the HAck message. Itcan also be so arranged that, with regard to the neighbor subnetinformation acquiring means 2205, 2305 and 2405, in the sixth to theeighth embodiments (PAR21 shown in each of FIGS. 15, 17 and 19), PAR21can acquire the external transmission address relating to the subnet 30at the time of transmitting and receiving the HI message and the HAckmessage.

10th Embodiment

Next, description will be given on the tenth embodiment of the presentinvention. The operation in the tenth embodiment of the invention is thesame as the operation explained in the above referring to the sequencechart of FIG. 21, and detailed description is not given here.

FIG. 25 is a block diagram to show an example of arrangement of PAR inthe tenth embodiment of the invention. Although the functions of PAR21are shown by blocks in FIG. 25, these functions can be fulfilled byhardware and/or software. PAR21 shown in FIG. 25 comprises receivingmeans 3201, transmitting means 3202, FBU processing means 3203, FBAckgenerating means 3204, and neighbor subnet information acquiring means3205. The neighbor subnet information acquiring means 3205 has HIgenerating means 3206 for generating the HI message, HAck processingmeans 3207 for performing processing of the HAck message, and externaltransmission address notifying message processing means 3208 forprocessing the external transmission address notifying message includingthe external transmission address received from NAR31.

In PAR21 as to be explained in the tenth embodiment of the invention,when a request of the external transmission address is received by anFBU message from MN10, PAR21 transmits and receives the HI message andthe HAck message and acquires the external transmission address relatingto the subnet 30, which is the handover destination of MN10, and ittransmits FBAck message including the external transmission address toMN10. Thus, this can be regarded as one aspect of PAR21, which has beenexplained in the fifth embodiment in the above.

Description will be given below on the arrangement of PAR21 shown inFIG. 25 by comparing with the arrangement of PAR21 shown in FIG. 13.Similarly to the ninth embodiment as given above, PAR21 shown in FIG. 25has receiving means 3201, transmitting means 3202, FBU processing means3203 and FBAck generating means 3204, and these are basically the sameas the receiving means 2101, the transmitting means 2102, the FBUprocessing means 2103, and the FBAck generating means 2104.

The HI generating means 3206 of PAR21 shown in FIG. 25 is the same asthe HI generating means 3106 shown in FIG. 22, and this is the means togenerate an HI message in the conventional FMIP or an HI messageincluding the external transmission address request. Similarly to theninth embodiment, PAR21 transmits the HI message generated by the HIgenerating means 3206 to NAR31 and receives the HAck message, which is aresponse of the HI message, and external transmission address notifyingmessage including the external transmission address relating to thesubnet 30. In PAR21, the HAck message received from NAR31 is the same asthe HAck message defined in the conventional FMIP, and it is processedby the HAck processing means 3207. On the other hand, the externaltransmission address notifying message received from NAR31 is processedby the external transmission address notifying message processing means3208. The external transmission address notifying message processingmeans 3208 extracts the external transmission address relating to thesubnet 30 from the external transmission address notifying message andsupplies this external transmission address relating to the subnet 30 asextracted to the FBAck generating means 3204. In so doing, the FBAckgenerating means 3204 can generate an FBAck message including theexternal transmission address of the subnet 30.

FIG. 26 is a block diagram to show an example of arrangement of NAR inthe tenth embodiment of the present invention. Although the functions ofNAR31 is shown by blocks in FIG. 26, these functions can be fulfilled byhardware and/or software. NAR31 shown in FIG. 26 comprises receivingmeans 3211, transmitting means 3212, HI processing means 3213, HAckgenerating means 3214, subnet information acquiring means 3215, subnetinformation storing means 3216, and external transmission addressnotifying message generating means 3217.

Similarly to NAR31 shown in FIG. 23, in NAR31 shown in FIG. 26 when HImessage is received from PAR21, the HI processing means 3213 performsprocessing of the HI message and instructs the generation of the HAckmessage to the HAck generating means 3214 and requests the acquisitionof the external transmission address relating to the subnet 30 to thesubnet information acquiring means 3215, and the subnet informationacquiring means 3215 acquires the external transmission address relatingto he subnet 30. Then, the subnet information acquiring means 3215notifies the result of the acquisition to the external transmissionaddress notifying message generating means 3217. As a result, the HAckgenerating means 3214 can generate the external transmission addressnotifying message including the external transmission address relatingto the subnet 30.

FIG. 27A represents diagrams to show the request information of theexternal transmission address to be given and taken between PAR shown inFIG. 25 and NAR shown in FIG. 26. FIG. 27B represents diagrams to showan example of data arrangement of the notifying information of theexternal transmission address. It is so arranged that PAR21 transmitsthe HI message in the conventional FMIP shown in FIG. 27A and the HImessage including the request of the external transmission address.Also, it is so arranged that NAR31 transmits the HAck message in theconventional FMIP and the external transmission address notifyingmessage including the external transmission address relating to thesubnet 30.

As described above, according to the tenth embodiment of the presentinvention, when MN10 executes the handover to different subnets 30, whenreceiving the external transmission address relating to the subnet 30from MN10, PAR21 transmits the HI message to NAR31 and requests theexternal transmission address relating to the subnet 30. Then, NAR31 cannotify the external transmission address relating to the subnet 30 bytransmitting an external transmission address notifying messagedifferent from the HAck message, which is its response message. PAR21notifies the external transmission address relating to the subnet 30 asacquired to MN10. Then, MN10 can acquire the external transmissionaddress relating to the subnet 30 connected after the handover and canquickly execute packet transmission to outside immediately after thehandover.

Description has been given in the above on a case where it is soarranged in PAR21 shown in FIG. 25 that, similarly to the case of theninth embodiment, the neighbor subnet information acquiring means 2105can acquire the external transmission address relating to the subnet 30at the time of transmitting and receiving of the HI message and the HAckmessage in PAR21 in the fifth embodiment (PAR21 as shown in FIG. 13).However, it can also be so arranged that, with regard to the neighborinformation acquiring means 2205, 2305 and 2405, PAR21 in the sixth tothe eighth embodiments (PAR21 shown in each of FIGS. 15, 17 and 19) canacquire the external transmission address relating to the subnet 30 atthe time of transmitting and receiving of the HI message and the HAckmessage.

11th Embodiment

Next, description will be given on the eleventh embodiment of thepresent invention. The operation in the eleventh embodiment of theinvention is the same as the operation explained in the above byreferring to the sequence chart of FIG. 21, and detailed description isnot given here.

FIG. 28 is a block diagram to show an example of arrangement of PAR inthe eleventh embodiment of the present invention. Although the functionsof PAR2 are shown by blocks in FIG. 28, these functions can be fulfilledby hardware and/or software. PAR21 shown in FIG. 28 comprises receivingmeans 3301, transmitting means 3302, FBU processing means 3303, FBAckgenerating means 3304, and neighbor information acquiring means 3305.The neighbor subnet information acquiring means 3305 has HI generatingmeans 3306 for generating HI message, HAck processing means 3307 forperforming processing of HAck message, and external transmission addressrequesting message generating means 3308 for generating externaltransmission address requesting message to request external transmissionaddress to NAR31.

PAR21 as explained in the eleventh embodiment of the invention may beregarded as one aspect of PAR21 explained in connection with the fifthembodiment. The reasons are as follows: When a request of the externaltransmission address is received from MN10 by FBU message, HI messageand HAck message are given, and PAR21 acquires the external transmissionaddress relating to the subnet 30, which is handover destination of MN10by utilizing the transmitting and the receiving of the HI message andthe HAck message, and an FBAck message including the externaltransmission address is transmitted to MN10.

Description will be given below on the arrangement of PAR21 shown inFIG. 28 by comparing with the arrangement of PAR21 shown in FIG. 13.Similarly to the ninth embodiment as given above, the receiving means3301, the transmitting means 3302, the FBU processing means 3303, andthe FBAck generating means 3304 of PAR21 shown in FIG. 28 are basicallythe same as the receiving means 2101, the transmitting means 2102, theFBU processing means 2103, and the FBAck generating means 2104 shown inFIG. 13 respectively.

The HI generating means 3306 of PAR21 shown in FIG. 28 is the same asthe HI generating means 3106 shown in FIG. 22, and it is the means togenerate the HI message in the conventional FMIP or the HI messageincluding the request of the external transmission address. Afterprocessing the FBU message from MN10, the FBU processing means 3303 ofPAR21 sends an instruction to generate the HI message to the HIgenerating means 3306 and also gives an instruction to generate theexternal transmission address requesting message to request the externaltransmission address relating to the subnet 30 to the externaltransmission address requesting message generating means 3308, and ittransmits the HI message generated at the HI generating means 3306 andthe external transmission address requesting message generated at theexternal transmission address requesting message generating means 3308.NAR31 acquires the external transmission address relating to the subnet30 according to the HI message received from PAR21 and the externaltransmission address requesting message and generates an HAck messageincluding the result of the acquisition and transmits it to PAR21. TheHAck processing means 3307 of PAR21 extracts the external transmissionaddress relating to the subnet 30 from the HAck message received fromNAR31 and sends the external transmission address relating to the subnet30 as extracted to the FBAck generating means 3304. As a result, theFBAck generating means 3304 can generate the FBAck message including theexternal transmission address of the subnet 30.

FIG. 29 is a block diagram to show an example of arrangement of NAR inthe eleventh embodiment of the present invention. Although the functionsof NAR31 are shown by blocks in FIG. 29, these functions can befulfilled by hardware and/or software. NAR31 shown in FIG. 29 comprisesreceiving means 3311, transmitting means 3312, HI processing means 3313,HAck generating means 3314, subnet information acquiring means 3315,subnet information storing means 3316, and external transmission addressrequesting message processing means 3317.

In NAR31 shown in FIG. 29, when the HI message and the externaltransmission address requesting message are received from PAR21, the HIprocessing means 3313 processes the HI message and gives an instructionto generate HAck message to the HAck generating means 3314. The externaltransmission address requesting message processing means 3317 receivesthe external transmission address requesting message and requests theacquisition of the external transmission address relating to the subnet30 to the subnet information acquiring means 3315. Then, similarly tothe ninth embodiment as given above, the subnet information acquiringmeans 3315 acquires the external transmission address relating to thesubnet 30 and notifies the result of the acquisition to the HAckgenerating means 3314. As a result, the HAck generating means 3314 cangenerate the HAck message including the external transmission addressrelating to the subnet 30.

FIG. 30A represents diagrams to show the request information of theexternal transmission address to be given and taken between PAR shown inFIG. 28 and NAR shown in FIG. 29. FIG. 30B is a diagram to show anexample of data arrangement of the notifying information of the externaltransmission address. PAR21 is so arranged that it transmits the HImessage in the conventional FMIP shown in FIG. 30A and the externaltransmission address requesting message. NAR31 is so arranged that ittransmits the HAck message including the external transmission addressrelating to the subnet 30 to PAR21 as shown in FIG. 30B.

As described above, according to the eleventh embodiment of the presentinvention, when MN10 executes the handover to different subnets 30,after receiving the external transmission address relating to the subnet30 from MN10, PAR21 requests the external transmission address relatingto the subnet 30 by transmitting an external transmission addressrequesting message different from the HI message to NAR31. NAR31 cannotify the external transmission address relating to the subnet 30 bytransmitting the HAck message. By notifying the external transmissionaddress relating to the subnet 30 as acquired to MN10, PAR21 acquiresthe external transmission address relating to the subnet 30 connectedafter the handover on a link of the subnet connected before the handoverand can quickly execute packet transmission to outside immediately afterthe handover.

Similarly to the case of the ninth embodiment as given above,description has been given on a case where it is so arranged in PAR21shown in FIG. 28 that neighbor subnet information acquiring means 2105in PAR21 of the fifth embodiment (PAR21 shown in FIG. 13) can acquirethe external transmission address relating to the subnet 30 at the timeof transmitting and receiving of the HI message and the HAck message.However, it can also be so arranged that the external transmissionaddress relating to the subnet 30 can be acquired at the time oftransmitting and receiving of the HI message and the HAck message by theneighbor subnet information acquiring means 2205, 2305 and 2405 in PAR21of the sixth to the eighth embodiments as given above (PAR21 in each ofFIGS. 15, 17 and 19).

12th Embodiment

Next, description will be given on the twelfth embodiment of the presentinvention. The operation in the twelfth embodiment of the invention isthe same as the operation as explained referring to the sequence chartof FIG. 21, and detailed description is not given here.

FIG. 31 is a block diagram to show an arrangement of PAR in the twelfthembodiment of the invention. Although the functions of PAR21 are shownby blocks in FIG. 31, these functions can be fulfilled by hardwareand/or software. PAR21 shown in FIG. 31 comprises receiving means 3401,transmitting means 3402, FBU processing means 3403, FBAck generatingmeans 3404, and neighbor subnet information acquiring means 3405. Theneighbor subnet information acquiring means 3405 has the HI generatingmeans 3406 for generating an HI message, HAck processing means 3407 forprocessing the HAck message, external transmission address requestingmessage generating means 3408 for generating the external transmissionaddress requesting message to request the external transmission addressto NAR31, and external transmission address notifying message processingmeans 3409 for performing processing of external transmission addressnotifying message including the external transmission address receivedfrom NAR31.

In PAR21 as explained in the twelfth embodiment of the presentinvention, when a request of the external transmission address isreceived by FBU message from MN10, HI message and HAck message aregiven, and PAR21 acquires the external transmission address relating tothe subnet 30, which is the handover destination of MN10, by utilizingthe transmitting and the receiving of the HI message and the HAckmessage and transmits the FBAck message including the externaltransmission address to MN10. Thus, this may be regarded as one aspectof PAR21 as explained in connection with the fifth embodiment in theabove.

Description will be given below on the arrangement of PAR21 shown inFIG. 31 by comparing with the arrangement of PAR21 shown in FIG. 13.Similarly to the case of the ninth embodiment as given above, thereceiving means 3401, the transmitting means 3402, the FBU processingmeans 3403, and the FBAck generating means 3404 of PAR31 shown in FIG.31 are basically the same as the receiving means 2101, the transmittingmeans 2102, the FBU processing means 2103, and the FBAck generatingmeans 2104 as shown in FIG. 13 respectively.

Also, the HI generating means 3406 and the external transmission addressrequesting message generating means 3408 of PAR21 shown in FIG. 31 arethe same as the HI generating means 3306 and the external transmissionaddress requesting message generating means 3308. Further, the HAckprocessing means 3407 and the external transmission address notifyingmessage processing means 3409 of PAR21 shown in FIG. 31 are the same asthe HAck processing means 3207 and the external transmission addressnotifying message processing means 3208 as shown in FIG. 25respectively.

Specifically, the FBU processing means 3403 of PAR21 sends aninstruction to generate the HI message to the HI generating means 3406after processing the FBU message from MN10. It also gives an instructionto generate an external transmission address requesting message torequest the external transmission address relating to the subnet 30 tothe external transmission address requesting message generating means3408. Also, it transmits the HI message generated at the HI generatingmeans 3406 and the external transmission address requesting messagegenerated at the external transmission address requesting messagegenerating means 3408.

On the other hand, NAR31 acquires the external transmission addressrelating to the subnet 30 according to the HI message received fromPAR21 and to the external transmission address requesting message. Then,it generates an HAck message, which is a response to the HI message, andalso the external transmission address notifying message including theexternal transmission address relating to the subnet 30 and transmitsthese messages to PAR21.

Then, PAR21 performs the same processing as the processing in theconventional FMIP to the HI message. With regard to the externaltransmission address notifying message, it extracts the externaltransmission address relating to the subnet 30 from the externaltransmission address notifying message by the external transmissionaddress notifying message processing means 3409 and sends the externaltransmission address relating to the subnet 30 as extracted to the FBAckgenerating means 3404. As a result, the FBAck generating means 3404 cangenerate FBAck message including the external transmission address ofthe subnet 30.

FIG. 32 is a block diagram to show an example of arrangement of NAR inthe twelfth embodiment of the present invention. Although the functionsof NAR31 are shown by blocks in FIG. 32, these functions can befulfilled by hardware and/or software. NAR31 shown in FIG. 32 comprisesreceiving means 3411, transmitting means 3412, HI processing means 3413,HAck generating means 3414, subnet information acquiring means 3415,subnet information storing means 3416, external transmission addressrequesting message processing means 3417, and external transmissionaddress notifying message generating means 3418.

The external transmission address requesting message processing means3417 of NAR31 shown in FIG. 32 is the same as the external transmissionaddress requesting message processing means 3317 of NAR31 shown in FIG.29, and the external transmission address notifying message generatingmeans 3418 of NAR31 is the same as the external transmission addressnotifying message generating means 3217 of NAR31 shown in FIG. 26.Specifically, when the HI message and the external transmission addressrequesting message are received from PAR21, HI processing means 3413performs processing on the HI message and NAR31 shown in FIG. 32 givesan instruction to generate the HAck message to the HAck generating means3414. On the other hand, the external transmission address requestingmessage processing means 3417 receives the external transmission addressrequesting message and requests the acquisition of the externaltransmission address relating to the subnet 30 to the subnet informationacquiring means 3415. Then, the subnet information acquiring means 3415acquires the external transmission address relating to the subnet 30 andnotifies the result of the acquisition to the external transmissionaddress notifying message generating means 3418. Then, the externaltransmission address notifying message generating means 3418 cangenerate the external transmission address notifying message includingthe external transmission address relating to the subnet 30 differentfrom the HAck message.

FIG. 33A represents diagrams to show the request information of theexternal transmission address to be given and taken between PAR shown inFIG. 31 and NAR31 shown in FIG. 32. FIG. 33B represents diagrams to showan example of data arrangement of the notifying information of theexternal transmission address. PAR21 is so arranged that it transmits HImessage in the conventional FMIP as shown in FIG. 33A and the externaltransmission address requesting message to NAR31. NAR31 is so arrangedthat it transmits the HAck message in the conventional FMIP and theexternal transmission address notifying message to PAR21 as shown inFIG. 33B.

As described above, according to the twelfth embodiment of the presentinvention, when MN10 executes the handover to different subnets 30, uponreceipt of the external transmission address relating to the subnet 30from MN10, PAR21 requests the external transmission address relating tothe subnet 30 by transmitting an external transmission addressrequesting message different from the HI message to NAR31. Then, NAR31can notify the external transmission address relating to the subnet 30by transmitting the external transmission address notifying messagedifferent from the HAck message. Then, MN10 acquires the externaltransmission address relating to the subnet 30 connected after thehandover on a link of the subnet 20 connected before the handover, andPAR21 notifies the external transmission address relating to the subnet30 as acquired, and MN10 can quickly execute packet transmission tooutside immediately after the handover.

Description has been given on a case in PAR21 shown in FIG. 31 where,similarly to the case of the ninth embodiment as describe above, PAR21in the fifth embodiment as given above (PAR21 shown in FIG. 13) canacquire the external transmission address relating to the subnet 30 whenthe neighbor subnet information acquiring means 2105 transmits andreceives the HI message and the HAck message. However, it can also be soarranged that the external transmission address relating to the subnet30 can be acquired when the HI message and the HAck message istransmitted and received by the neighbor subnet information acquiringmeans 2205, 2305 and 2405 in PAR21 in the sixth to the eighthembodiments as given above (PAR21 in each of FIGS. 15, 17 and 19).

Also, in the first to the twelfth embodiments as given above, NAR31belonging to the subnet 30 or other router (e.g. default router 37) cannotify, in addition to the external transmission address relating to thesubnet 30, an arbitrary information included in the RA message to besent within the subnet 30.

In particular, the types of information as given below among arbitraryinformation included in RA message, may be the types of information,which deserve to be provided to MN10 before the handover as additionalinformation. For example, “CureHopLimit”, in which the number of hops inthe packet to be transmitted from MN10 is defined is information,deserves to be provided to MN10 as additional information. This“CureHopLimit” is information to be described in IPv6 header when MN10transmits packet, and MN10 must know this value in advance. Also,“RouterLifetime”, in which the time to be used as default router isdefined, for instance, is information which deserves to be provided toMN10 as additional information. Further, “ReachableTime”, in whichtransmission interval of NS (Neighbor Solicitation) is defined asutilized in Neighbor Unreachability Detection algorithm is alsoinformation, which deserves to be used as additional information.

Also, “RetransmissionTime”, in which retransmission interval is definedin case, in which there is no response of NS received at “ReachableTime”as used in “Address Resolution or Neighbor Unreachability Detectionalgorithm” may also be regarded as information, which deserves to beused as additional information. Further, “ValidLifetime”, in whichusable time of network prefix is defined, may also be regarded asinformation, which deserves to be used as additional information. Also,“PreferredLifetime”, in which the period when the use of network prefixis desirable is defined, may also be regarded as information, whichdeserves to be used as additional information. Further, “MTU option”, inwhich the length of MTU (Maximum Transmission Unit) of packettransmitted by MN10 is defined, may be regarded as information, whichdeserves to be used as additional information.

13th Embodiment

Next, description will be given on the thirteenth embodiment of thepresent invention. FIG. 34 is a sequence chart to show principalprocessing common to the thirteenth and the fourteenth embodiments ofthe present invention. The sequence chart shown in FIG. 34 shows onlythe principal processing according to the present invention, and thetechnique to be explained in connection with the thirteenth embodimentof the invention can be executed in combination with the first or thesecond operation mode in FMIP as shown in FIG. 41 and FIG. 42.

In the sequence chart shown in FIG. 34, after MN10 executes L2 handoverto the subnet 30 (Step S401), information to request the externaltransmission address is transmitted in addition to FNA message (StepS403). In the present invention, regardless of whether the FBU messageis included in the FNA message transmitted by MN10 or not, any of thefirst and the second operation modes in the conventional FMIP may beexecuted.

NAR31 receives the FNA message from MN10 and performs the processing asrequired (e.g. verification of FNA message or processing to startforwarding the packet in buffering), and it acquires the externaltransmission address relating to the subnet 30 (Step S405) and notifiesthe external transmission address to MN10 (Step S407). More concretely,NAR31 notifies the link local address of its own or retrieves accessrouter within the same subnet 30 and acquires and notifies a link localaddress of a default router 37 belonging to the subnet 30 or it canacquire and notify a link local address of the default router 37belonging to the subnet 30 from the information already retrieved(information retained at NAR31).

As a result, MN10 can acquire the external transmission address relatingto the subnet 30 from NAR31 immediately after the handover. That is,MN10 can quickly execute packet transmission to outside (e.g. CN40) inthe subnet 30 by setting up a link local address of NAR31 acquired bythe above procedure or a link local address of the default router 37 inthe transmission packet immediately after executing the handover to thelink of the subnet 30.

FIG. 35 is a block diagram to show an example of the arrangement of NARin the thirteenth embodiment of the present invention. Although thefunctions of NAR31 are shown by blocks in FIG. 35, these functions canbe fulfilled by hardware and/or software. NAR31 shown in FIG. 35comprises receiving means 4101, transmitting means 4102, FNA processingmeans 4103, RA generating means 4104, subnet information acquiring means4105, and subnet information storing means 4106.

The FNA message received from MN10 by NAR31 is processed by the FNAprocessing means 4103, and an instruction to acquire the externaltransmission address relating to the subnet 30 is given to the subnetinformation acquiring means 4105 from the FNA processing means 4103. Thesubnet information acquiring means 4105 acquires the externaltransmission address relating to the subnet 30 by communicating with therouter in the subnet or by reading the information stored in the subnetinformation storing means 4106, and the result of the acquisition isnotified to the RA generating means 4104. The RA generating means 4104generates an RA (Router Advertisement) message including the externaltransmission address relating to the subnet 30 and transmits it to MN10.As a result, MN10 can quickly acquire the external transmission addressrelating to the subnet 30 immediately after executing the handover tothe link of a new subnet 30.

FIG. 36A represents diagrams to show the request information of theexternal transmission address from MN to be processed in NAR shown inFIG. 35. FIG. 36B is a diagram to show an example of data arrangement ofthe notifying information of the external transmission address to betransmitted to MN. As shown in FIG. 36A, NAR31 receives a conventionalFNA message (In this case, the conventional FNA message plays a role ofinformation to request the external transmission address.) or an FNAmessage including a request of the external transmission address (e.g.information belonging to RS (Router Solicitation) message). Then, ittransmits an RA message including the conventional external transmissionaddress as shown in FIG. 36B.

Therefore, in case where it is so arranged that the RA message istransmitted to MN10, to which NAR31 has sent an FNA message added withthe information to instruct the request of the external transmissionaddress, MN10 must have the means to insert the information to instructthe request of the external transmission address within the FNA message,although not shown in the figures.

As described above, according to the thirteenth embodiment of thepresent invention, when MN10 executes the handover to different subnets30, MN10 requests the external transmission address relating to thesubnet 30 by transmitting the FNA message to NAR31 and can notify theexternal transmission address relating to the subnet 30 by transmittingthe RA message to MN10 in response to this request. Then, MN10 canacquire the external transmission address relating to the subnet 30 tobe newly connected immediately after the handover and can quicklyexecute packet transmission to outside.

14th Embodiment

Next, description will be given on the fourteenth embodiment of thepresent invention. The operation in the fourteenth embodiment of thepresent invention is the same as the operation as explained abovereferring to the sequence chart of FIG. 34, and detailed description isnot given here.

FIG. 37 is a block diagram to show an example of arrangement of NAR inthe fourteenth embodiment of the present invention. Although thefunctions of NAR31 are shown by blocks in FIG. 37, these functions canbe fulfilled by hardware and/or software. NAR31 shown in FIG. 37comprises receiving means 4201, transmitting means 4202, FNA processingmeans 4203, RS processing means 4204, subnet information acquiring means4205, subnet information storing means 4206, and RA generating means4207. NAR31 shown in FIG. 37 has almost the same arrangement as that ofthe conventional access router, while it differs in that it can alsogenerate the RA message including not only a link local address of NAR31but also a link local address of a default router 37 of the subnet 30,to which NAR31 belongs. Also, it is also possible to use a conventionalaccess router, which notifies only the link local address of NAR31itself as NAR31.

FIG. 38A represents diagrams to show the request information of theexternal transmission address from MN to be processed in NAR shown inFIG. 37. FIG. 38B is a diagram to show an example of data arrangement ofthe notifying information of the external transmission addresstransmitted to MN. As shown in FIG. 38B, the RA message including theexternal transmission address relating to the subnet 30 is transmittedto MN10.

FIG. 39 is a block diagram to show an example of arrangement of MN inthe fourteenth embodiment of the present invention. Although thefunctions of MN10 are shown by blocks in FIG. 39, these functions can befulfilled by hardware and/or software. MN10 shown in FIG. 39 comprisesradio receiving means 4211, radio transmitting means 4212, L2 handovernotifying means 4213, FNA generating means 4214, RS generating means4214, route setting means 4216, and packet generating means 4217.

In case information to indicate that L2 handover is executed by the L2handover notifying means 4213 has been notified to the FNA generatingmeans 4214 and the RS generating means 4215, the FNA generating means4214 and the RS generating means 4215 generate the FNA message and theRS message independently from each other and transmit the message toNAR31 via the radio transmitting means 4212.

NAR31 processes the FNA message and the RS message received from MN10via the receiving means 4201 at the FNA processing means 4203 and the RSprocessing means 4204. At the FNA processing means 4203, the sameprocessing as the processing of the FNA message in the conventional FMIPis performed. Also, the RS processing means 4204 notifies the receivingof RS from MN10 to the subnet information acquiring means 4205. Takingthe opportunity of this notification, the external transmission addressrelating to the subnet 30 as acquired at the subnet informationacquiring means 4205 is supplied to the RA generating means 4207. The RAgenerating means 4207 generates an RA message including the externaltransmission address relating to the subnet 30 and transmits it to MN10via the transmitting means 4202.

MN10 receives RA message from NAR31 via the radio receiving means 4211.Then, at the route setting means 4216, it extracts a link layer addressof NAR31 and/or of a default router 37 from within the RA message andsets up this link layer address as a route to send the packet outside ofthe subnet 30, for instance. As a result, when the transmission data ispacketized at the packet generating means 4217, for instance, MN10acquires the external transmission address relating to the subnet 30newly connected immediately after the handover by setting the externaltransmission address at the header of the transmission packet and canquickly execute packet transmission to outside.

As described above, according to the fourteenth embodiment of thepresent invention, when MN10 executes the handover to different subnets30, it can request the external transmission address relating to thesubnet 30 by transmitting the RS message together with the FNA messageto NAR31. In response to this request, NAR31 can notify the externaltransmission address relating to the subnet 30 by transmitting the RAmessage to MN10. MN10 can acquire the external transmission addressrelating to the subnet 30 newly connected immediately after the handoverand can quickly execute packet transmission to outside.

15th Embodiment

Next, description will be given on the fifteenth embodiment of thepresent invention. FIG. 40 is a sequence chart to show principalprocessing in the fifteenth embodiment of the invention. Compared withthe sequence chart of FIG. 34, the sequence chart of FIG. 40 isdifferent in that, by multi-casting the FNA message and/or the RSmessage, the FNA message and/or the RS message can reach not only NAR31but also a plurality of routers within the subnet 30 including a defaultrouter 37 (Steps S503 and S505), and the RA message is transmitted toMN10 from the plurality of routers (Steps S511 and S513).

In this case, MN10 receives the RA message from a plurality of routers.In the RA message sent from each router, various types of informationsuch as information to identify the default router 37 are described.Therefore, MN10 can identify the default router 37 from the informationin the RA message received from each router and can acquire the linklocal address of the default router 37.

For instance, in the thirteenth and the fourteenth embodiments as givenabove, in case it is so arranged that, when at least one of the FNAmessage or the FNA message including the request of the externaltransmission address of the RS message is multi-cast within the subnet30 from MN10 and when a router present in the subnet 30 (in particular,NAR31 and the default router 37) receives the message, and the RAmessage including the link layer address of its own router istransmitted to MN10 or is sent in multi-cast, and the fifteenthembodiment of the present invention can be achieved. In case the linklocal address of the default router 37 is notified from the defaultrouter 37 to MN10, it is not necessary to arrange so that the link localaddress of the default router 37 is notified from NAR31 to MN10.

INDUSTRIAL APPLICABILITY

The communication system, the mobile terminal, and the access routeraccording to the present invention can provide such effects that themobile terminal can quickly execute packet transmission to outsideimmediately after the handover when executing the handover betweensubnets. This technique can be applied to the handover to performcontinuous IP communication. In particular, it is useful for theapplication in the communication system provided with FMIP or in casethe mobile terminal executes data distribution.

1. A communication system, comprising a first access router belonging toa first subnet and a second access router belonging to a second subnetdifferent from said first subnet, said first access router and saidsecond access router being connected via IP network, and a mobileterminal is connected to said first subnet or said second subnet viaradio communication, wherein: the mobile terminal connected to saidfirst subnet requests a link local address of said second access routeror of a default router in said second subnet to said first access routerunder the condition being connected to said first subnet after decidingthe execution of handover to said second subnet; and said first accessrouter is arranged to provide information included in an RA message sentin said second subnet by said second access router or said defaultrouter together with said link local address to said mobile terminal. 2.The communication system according to claim 1, wherein said mobileterminal is arranged to refer to said link local address whentransmitting packet to outside of said second subnet after executing thehandover from said first subnet to said second subnet.
 3. Thecommunication system according to claim 1, wherein said mobile terminalis arranged to request said link local address to said first accessrouter when transmitting a message P to request information relating tosaid second access router.
 4. The communication system according toclaim 3, wherein said mobile terminal is arranged to add information toinstruct a request of said link local address in said message P or totransmit information to request said link local address different fromsaid message P to said first access router, said first access routeracquires said link local address relating to a subnet specified byinformation in said message P, and specified by at least one ofinformation to request said link local address and information in saidmessage P received from said mobile terminal, and transmits a message Qor a notifying message different from said message Q to said mobileterminal by incorporating said link local address in the message Q,which is a response message of said message P, or the notifying messagedifferent from said message Q.
 5. A communication system, comprising afirst access router belonging to a first subnet and a second accessrouter belonging to a second subnet different from said first subnet,said first access router and said second access router being connectedvia IP network, and a mobile terminal is connected to said first subnetor said second subnet via radio communication, wherein: the mobileterminal connected to said first subnet requests a link local address ofsaid second access router or of a default router in said second subnetto said first access router under the condition being connected to saidfirst subnet after deciding the execution of handover to said secondsubnet; and said first access router acquires said link local addressrelating to the subnet specified by information in a message P when themessage P to request information relating to said second access routeris received from said mobile terminal and transmits a message Qincluding said link local address to said mobile terminal byincorporating said link local address in the message Q, which is aresponse message of said message P.
 6. A communication system,comprising a first access router belonging to a first subnet and asecond access router belonging to a second subnet different from saidfirst subnet, said first access router and said second access routerbeing connected via IP network, and a mobile terminal is connected tosaid first subnet or said second subnet via radio communication,wherein: the mobile terminal connected to said first subnet requests alink local address of said second access router or of a default routerin said second subnet to said first access router under the conditionbeing connected to said first subnet after deciding the execution ofhandover to said second subnet; and said first access router acquiressaid link local address relating to the subnet specified by informationin a message P when the message P to request information relating tosaid second access router is received from said mobile terminal, andtransmits a notifying message including said link local address to saidmobile terminal by incorporating said link local address in thenotifying message different from the message Q, which is a responsemessage of said message P.
 7. A communication system, comprising a firstaccess router belonging to a first subnet and a second access routerbelonging to a second subnet different from said first subnet, saidfirst access router and said second access router being connected via IPnetwork, and a mobile terminal is connected to said first subnet or saidsecond subnet via radio communication, wherein: the mobile terminalconnected to said first subnet is arranged to request a link localaddress of said second access router or of a default router in saidsecond subnet to said first access router when transmitting a message Rto request to forward a packet addressed to said mobile terminal to saidsecond access router under the condition being connected to said firstsubnet after deciding the execution of the handover to said secondsubnet; and said first access router is arranged to provide said linklocal address to said mobile terminal.
 8. The communication systemaccording to claim 7, wherein said mobile terminal is arranged to addinformation to instruct a request of said link local address in saidmessage R or to transmit information to request said link local addressdifferent from said message R to said first access router, said firstaccess router acquires said link local address relating to the subnetspecified by at least one of information in said message R, a message Pto request information relating to said second access router, andinformation in said message P received from said mobile terminal alreadybefore the receiving of said message R, and is arranged to transmit amessage S including said link local address to said mobile terminal byincorporating said link local address in the message S, which is aresponse message of said message R.
 9. The communication systemaccording to claim 8, wherein said mobile terminal is arranged totransmit information to request said link local address different fromsaid message R to said first access router; and said first access routeris arranged to request said link local address to said second accessrouter when transmitting a message T to request the initiation ofhandover processing relating to said mobile terminal.
 10. Thecommunication system according to claim 8, wherein said mobile terminalis arranged to transmit information to request said link local addressdifferent from said message R to said first access router; and saidsecond access router is arranged to acquire said link local addressrelating to said second subnet, to which said second access routerbelongs, when said message T is received from said first access router,and to transmit a message U or a notifying message different from saidmessage U to said first access router by incorporating said link localaddress in the message U, which is a response message of said message Tor in the notifying message different from said message U.
 11. Thecommunication system according to claim 7, wherein said mobile terminalis arranged to add information to instruct a request of said link localaddress in said message R or to transmit information to request saidlink local address different from said message R to said first accessrouter, said first access router is arranged to acquire said link localaddress relating to the subnet specified by at least one of informationto request said link local address, information in said message Rreceived from said mobile terminal, information in said message Rreceived from said mobile terminal, a message P to request informationrelating to said second access, router, and information in said messageP received from said mobile terminal already before the receiving ofsaid message R, and transmits said notifying message including said linklocal address by incorporating said link local address in the notifyingmessage different from the message S, which is a response message ofsaid message R.
 12. The communication system according to claim 11,wherein said mobile terminal is arranged to add information to requestsaid link local address in said message R, and said first access routeris arranged to request said link local address to said second accessrouter when transmitting the message T to request the initiation ofhandover processing relating to said mobile terminal.
 13. Thecommunication system according to claim 12, wherein said first accessrouter is arranged to add information to indicate a request of said linklocal address in said message T or to transmit information to requestsaid link local address different from said message T to said secondaccess router, and said second access router is arranged to acquire saidlink local address relating to said second subnet, to which said secondaccess router belongs, and to transmit a message U or a notifyingmessage different from said message U to said first access router byincorporating said link local address in the message U, which is aresponse message of said message T, or in the notifying messagedifferent from said message U.
 14. The communication system according toclaim 11, wherein said mobile terminal is arranged to add information toindicate a request of said link local address in said message R; andsaid second access router is arranged to acquire said link local addressrelating to said second subnet, to which said second access routerbelongs, when said message T is received from said first access router,and to transmit a message U or a notifying message different from saidmessage U to said first access router by incorporating said link localaddress in the message U, which is a response message of said message T,or in the notifying message different from said message U.
 15. Acommunication system, comprising a first access router belonging to afirst subnet and a second access router belonging to a second subnetdifferent from said first subnet, said first access router and saidsecond access router being connected via IP network, and a mobileterminal is connected to said first subnet or said second subnet viaradio communication, wherein: the mobile terminal connected to saidfirst subnet requests a link local address of said second access routeror of a default router in said second subnet to said first access routerunder the condition being connected to said first subnet after decidingthe execution of handover to said second subnet; and when the message Rto request information relating to said second access router is receivedfrom said mobile terminal, said first access router acquires said linklocal address relating to the subnet specified by at least one ofinformation in said message R, a message P to request informationrelating to said second access router, and information in said message Preceived from said mobile terminal already before the receiving of saidmessage R, and to transmit a message S or a notifying message differentfrom said message S to said mobile terminal by incorporating said linklocal address in the message S, which is a response message of saidmessage R, or in a notifying message different from said message S. 16.A communication system, comprising a first access router belonging to afirst subnet and a second access router belonging to a second subnetdifferent from said first subnet, said first access router and saidsecond access router being connected via IP network, and a mobileterminal is connected to said first subnet or said second subnet viaradio communication, wherein: under the condition that said mobileterminal is connected to said first subnet, said first access router isarranged to transmit a message W to instruct the execution of handoverto said second subnet, which includes said link local address of saidsecond access router or of a default router in said second subnet, tosaid mobile terminal.
 17. The communication system according to claim16, wherein said first access router is arranged to provide informationincluded in an RA message sent in said second subnet by said secondaccess router or said default router together with said link localaddress to said mobile terminal.
 18. The communication system accordingto claim 16, wherein said mobile terminal is arranged to refer to saidlink local address when transmitting a packet to outside of said secondsubnet after executing the handover from said first subnet to saidsecond subnet.
 19. A mobile terminal in a communication system,comprising a first access router belonging to a first subnet and asecond access router belonging to a second subnet different from saidfirst subnet, said first access router and said second access routerbeing connected via IP network, a mobile terminal arranged to beconnected to said first subnet or said second subnet via radiocommunication, wherein there are provided: means for requesting a linklocal address of said second access router or of a default router insaid second subnet to said first access router under the condition beingconnected to said first subnet when the handover is executed from saidfirst subnet to said second subnet; means for receiving said link localaddress from said first access router; and means for referring to saidlink local address when a packet is transmitted to outside of the saidsecond subnet after executing the handover from said first subnet tosaid second subnet.
 20. A mobile terminal in a communication system,comprising a first access router belonging to a first subnet and asecond access router belonging to a second subnet different from saidfirst subnet, said first access router and said second access routerbeing connected via IP network, a mobile terminal arranged to beconnected to said first subnet or said second subnet via radiocommunication, wherein there are provided: means for requesting a linklocal address of said second access router or of a default router insaid second subnet to said first access router when transmitting themessage P to request information relating to said second access routerunder the condition being connected to said first subnet in case thehandover is executed from said first subnet to said second subnet; andmeans for receiving said link local address from said first accessrouter.
 21. The mobile terminal according to claim 20, wherein there areprovided: means for adding information to instruct a request of saidlink local address in said message P or means for generating informationto request said link local address different from said message P and fortransmitting it to said first access router; means for receiving amessage Q including said link local address and being a response messageof said message P, or a notifying message different from said message Qand including said link local address from said first access router; andmeans for extracting said link local address from said message Q or fromsaid notifying message different from said message Q.
 22. A mobileterminal in a communication system, comprising a first access routerbelonging to a first subnet and a second access router belonging to asecond subnet different from said first subnet, said first access routerand said second access router being connected via IP network, a mobileterminal arranged to be connected to said first subnet or said secondsubnet via radio communication, wherein there are provided: means forrequesting a link local address of said second access router or of adefault router in said second subnet to said first access router underthe condition being connected to said first subnet when executing thehandover from said first subnet to said second subnet; means forreceiving a message Q including said link local address, which is aresponse message of said message P, or a notifying message differentfrom said message Q and including said link local address from saidfirst access router as a response after transmitting the message P torequest information relating to said second access router; and means forextracting said link local address from said message Q or from saidnotifying message.
 23. A mobile terminal in a communication system,comprising a first access router belonging to a first subnet and asecond access router belonging to a second subnet different from saidfirst subnet, said first access router and said second access routerbeing connected via IP network, a mobile terminal arranged to beconnected to said first subnet or said second subnet via radiocommunication, wherein there are provided: means for requesting a linklocal address of said second access router or of a default router insaid second subnet to said first access router when transmitting amessage R to request to forward a packet addressed to said mobileterminal to said second access router under the condition connected tosaid first subnet when executing the handover from said first subnet tosaid second subnet; and means for receiving said link local address fromsaid first access router.
 24. The mobile terminal according to claim 23,wherein there are provided: means for adding information to instruct arequest of said link local address in said message R, or means forgenerating information to request said link local address different fromsaid message R and for transmitting it to said first access router;means for receiving a message S including said link local address andbeing a response message of said message R or a notifying messagedifferent from said message S and including said link local address fromsaid first access router; and means for extracting said link localaddress from said message S or from said notifying message differentfrom said message S.
 25. A mobile terminal in a communication system,comprising a first access router belonging to a first subnet and asecond access router belonging to a second subnet different from saidfirst subnet, said first access router and said second access routerbeing connected via IP network, a mobile terminal arranged to beconnected to said first subnet or said second subnet via radiocommunication, wherein there are provided: means for requesting a linklocal address of said second access router or of a default router insaid second subnet to said first access router under the condition beingconnected to said first subnet when executing the handover from saidfirst subnet to said second subnet; means for receiving a message Sincluding said link local address and being a response message of saidmessage R or a notifying message including said link local address and anotifying message different from said message S from said first accessrouter as a response after transmitting the message R to request toforward a packet addressed to said mobile terminal to said second accessrouter; and means for extracting said link local address from saidmessage S or from said notifying message different from said message S.26. A mobile terminal in a communication system, comprising a firstaccess router belonging to a first subnet and a second access routerbelonging to a second subnet different from said first subnet, saidfirst access router and said second access router being connected via IPnetwork, a mobile terminal arranged to be connected to said first subnetor said second subnet via radio communication, wherein there is providedmeans for receiving a message W to instruct the execution of handover tosaid second subnet and including said link local address of said secondaccess router or of a default router in said second subnet from saidfirst access router.
 27. The mobile terminal according to claim 26,wherein there is provided means for receiving information included in anRA message sent in said second subnet by said second access router orsaid default router from said first access router.
 28. The mobileterminal according to claim 26, wherein there is provided means forreferring to said link local address when transmitting a packet tooutside of said second subnet after executing the handover from saidfirst subnet to said second subnet.
 29. An access router in acommunication system, comprising a first access router belonging to afirst subnet and a second access router belonging to a second subnetdifferent from said first subnet, said first access router and saidsecond access router being connected via IP network, said access routerbeing connected to said mobile terminal via radio communication, whereinthere are provided: means for receiving a request of a link localaddress of said second access router or a default router in said secondsubnet from said mobile terminal connected to said first subnet anddeciding that handover is executed to said second subnet; means foracquiring said link local address; and means for providing informationincluded in an RA message sent in said second subnet by said secondaccess router or by said default router together with said link localaddress to said mobile terminal.
 30. An access router in a communicationsystem, comprising a first access router belonging to a first subnet anda second access router belonging to a second subnet different from saidfirst subnet, said first access router and said second access routerbeing connected via IP network, said access router being connected tosaid mobile terminal via radio communication, wherein there areprovided: means for receiving a request of a link local address of saidsecond access router or of a default router in said second subnet fromsaid mobile terminal connected to said first subnet and deciding theexecution of handover to said second subnet when receiving a message Pto request information relating to said second access router from saidmobile terminal; means for acquiring said link local address; and meansfor providing said link local address to said mobile terminal.
 31. Theaccess router according to claim 30, wherein there are provided: meansfor acquiring said link local address relating to a subnet specified byat least one of information in said message P when information toinstruct a request of said link local address added in said message P isreceived as a request of said link local address from said mobileterminal, and by at least one of information to request said link localaddress and information in said message P received from said mobileterminal when information to request said link local address differentfrom said message P is received; and means for generating a message Q ora notifying message different from said message Q by incorporating saidlink local address in the message Q, which is a response message of saidmessage P, or in a notifying message different from said message Q, andfor transmitting said message Q or said notifying message different fromsaid message Q to said mobile terminal.
 32. An access router in acommunication system, comprising a first access router belonging to afirst subnet and a second access router belonging to a second subnetdifferent from said first subnet, said first access router and saidsecond access router being connected via IP network, said access routerbeing connected to said mobile terminal via radio communication, whereinthere are provided: means for receiving a request of a link localaddress of said second access router or of a default router in saidsecond subnet from said mobile terminal connected to said first subnetand deciding the execution of handover to said second subnet; means foracquiring said link local address relating to a subnet specified byinformation in a message P when the message P to request informationrelating to said second access router is received from said mobileterminal; and means for generating a message Q or a notifying messagedifferent from said message Q by incorporating said link local addressin said message Q or in the notifying message different from saidmessage Q, which is a response message of said message P, and fortransmitting said message Q or said notifying message different fromsaid message Q to said mobile terminal.
 33. An access router in acommunication system, comprising a first access router belonging to afirst subnet and a second access router belonging to a second subnetdifferent from said first subnet, said first access router and saidsecond access router being connected via IP network, said access routerbeing connected to said mobile terminal via radio communication, whereinthere are provided: means for receiving a link local address of saidsecond access router or of a default router in said second subnet when amessage R to request to forward a packet addressed to said mobileterminal from said mobile terminal to said second access router isreceived from said mobile terminal, which is connected to said firstsubnet and deciding the execution of handover to said second subnet;means for acquiring said link local address; and means for providingsaid link local address to said mobile terminal.
 34. The access routeraccording to claim 33, wherein there are provided: means for acquiringsaid link local address relating to a subnet specified by at least oneof information in said message P, a message P to request informationrelating to said second access router, and information in said message Preceived from said mobile terminal already before the receiving of saidmessage R when information to request said link local address added insaid message R is received as a request of said link local address fromsaid mobile terminal, or a subnet specified by at least one ofinformation in said message R received from said mobile terminal,information in said message R received from said mobile terminal, amessage P to request information relating to said second access router,and information in said message P received from said mobile terminalalready before the receiving of said message R when information torequest said link local address different from said message R isreceived; and means for generating a message S including said link localaddress by incorporating said link local address in the message S, whichis a response message of said message R, and for transmitting saidmessage S to said mobile terminal.
 35. The access router according toclaim 34, wherein there is provided means for requesting said link localaddress to said second access router when transmitting a message T torequest the initiation of the handover processing relating to saidmobile terminal in case information to request said link local addressadded in said message R is received as a request of said link localaddress from said mobile terminal.
 36. The access router according toclaim 35, wherein there are provided: means for adding information torequest said link local address in said message T or means forgenerating information to request said link local address different fromsaid message T, and for transmitting it to said second access router;means for receiving a message U, being a response message of saidmessage T and including said link local address or said notifyingmessage including said link local address; and means for extracting saidlink local address from said message U or said notifying message. 37.The access router according to claim 34, wherein there are provided:means for receiving a message U including said link local address andbeing a response message of said message T or a notifying messageincluding said link local address from said second access router as aresponse after transmitting said message T when information to requestsaid link local address added in the message R is received as a requestof said link local address from said mobile terminal; and means forextracting said link local address from said message U or from saidnotifying message.
 38. The access router according to claim 33, whereinthere are provided: means for acquiring said link local address relatingto a subnet specified by at least one of information in said message R,a message P to request information relating to said second accessrouter, and information in said message P received from said mobileterminal already before the receiving of said message R in caseinformation to request said link local address added in said message Ris received as a request of said link local address from said mobileterminal, or a subnet specified by at least one of information torequest said link local address, information in said message R receivedfrom said mobile terminal, a message P to request information relatingto said second access router, and information in said message P receivedfrom said mobile terminal already received before the receiving of saidmessage R in case information to request said link local addressdifferent from said message R is received; and means for generating saidnotifying message including said link local address by incorporatingsaid link local address in a notifying message different from a messageS, which is a response message of said message R, and for transmittingsaid notifying message to said mobile terminal.
 39. The access routeraccording to claim 38, wherein there is provided means for requestingsaid link local address to said second access router when transmitting amessage T to request the initiation of the handover processing relatingto said mobile terminal in case information to request said link localaddress added in said message R is received as a request of said linklocal address from said mobile terminal.
 40. The access router accordingto claim 38, wherein there are provided: means for receiving a message Ubeing a response message of said message T and including said link localaddress from said second access router as a response after transmittingsaid message T in case information to request said link local addressadded in said message R is received as a request of said link localaddress from said mobile terminal; and means for extracting said linklocal address from said message U or from said notifying message.
 41. Anaccess router in a communication system, comprising a first accessrouter belonging to a first subnet and a second access router belongingto a second subnet different from said first subnet, said first accessrouter and said second access router being connected via IP network,said access router being connected to said mobile terminal via radiocommunication, wherein there are provided: means for receiving a requestof a link local address of said second access router or of a defaultrouter in said second subnet from said mobile terminal connected to saidfirst subnet and deciding the execution of handover to said secondsubnet; means for acquiring said link local address relating to a subnetspecified by at least one of information in said message R, a message Pto request information relating to said second access router, andinformation in said message P received from said mobile terminal alreadybefore the receiving of said message R; and means for generating amessage S or a notifying message different from the message S byincorporating said link local address in the message S, which is aresponse message of said message R, or in the notifying messagedifferent from the message S, and for transmitting said message S orsaid notifying message different from the message S to said mobileterminal.
 42. An access router in a communication system, comprising afirst access router belonging to a first subnet and a second accessrouter belonging to a second subnet different from said first subnet,said first access router and said second access router being connectedvia IP network, said access router being connected to said mobileterminal via radio communication, wherein there are provided: means forreceiving a request of a link local address of said second access routeror of a default router in said second subnet from said mobile terminalconnected to said first subnet and deciding the execution of handover tosaid second subnet; means for acquiring said link local address; andmeans for transmitting a message including said link local address andfor instructing the execution of handover to said second subnet to saidmobile terminal.
 43. The access router according to claim 42, whereinthere is provided means for giving information included in an RA messagesent in said second subnet by said second access router or said defaultrouter together with said link local address to said mobile terminal.44. An access router, comprising a second access router belonging to asecond subnet different from a first subnet, to which a first accessrouter belongs, said second access router being connected with saidfirst access router via IP network, and being connected to a mobileterminal via radio communication, wherein there is provided: means forreceiving a request of said link local address of said second accessrouter or of a default router in said second subnet from said firstaccess router when a message T to request the initiation of the handoverprocessing relating to said mobile terminal from said first accessrouter is received.
 45. The access router according to claim 44, whereinit is so arranged that information included in an RA message sent insaid second subnet by said second access router or said default routeris provided together with said link local address to said first accessrouter.
 46. The access router according to claim 44, wherein there areprovided: means for receiving information to instruct a request of saidlink local address added in said message T as a request of said linklocal address from said first access router or for receiving informationto request said link local address different from said message T; meansfor acquiring said link local address in case said message T added withinformation to instruct a request of said link local address is receivedfrom said first access router or in case information to request saidlink local address is received from said first access router; and meansfor generating said message U or said notifying message different fromsaid message U including said link local address by incorporating saidlink local address in the message U, which is a response message of saidmessage T, or a notifying message different from said message U, and fortransmitting said message U or said notifying message different fromsaid message U to said first access router.
 47. The access routeraccording to claim 44, wherein there are provided: means for acquiringsaid link local address in case said message T is received from saidfirst access router; and means for generating s message U or a notifyingmessage different from said message U by incorporating said link localaddress in the message U, which is a response message of said message T,or in the notifying message different from said message U, and fortransmitting said message U or said notifying message different from themessage U to said first access router.